严肃游戏是计算机游戏一个新的发展方向，可以提供形象互动的模拟教学环境，已经广泛应用于科学教育、康复医疗、应急管理、军事训练等领域。虚拟角色是严肃游戏中模拟具有生命特征的图形实体，行为可信的虚拟角色能够提升用户使用严肃游戏的体验感。严肃游戏中的图形渲染技术已经逐步成熟，而虚拟角色行为建模的研究尚在初级阶段。可信的虚拟角色必须能够具有感知、情绪和行为能力。本文分别从游戏剧情与行为、行为建模方法、行为学习和行为建模评价等4个方面来分析虚拟角色行为建模研究。分析了有限状态机和行为树的特点，讨论了虚拟角色的行为学习方法。指出了强化学习的关键要素，探讨了深度强化学习的应用途径。综合已有研究，归纳了虚拟角色行为框架，该框架主要包括感觉输入、知觉分析、行为决策和动作4大模块。从情感计算的融入、游戏剧情和场景设计、智能手机平台和多通道交互4个角度讨论需要进一步研究的问题。虚拟角色的行为建模需要综合地考虑游戏剧情、机器学习和人机交互技术，构建具有自主感知、情绪、行为、学习能力、多通道交互的虚拟角色能够极大地提升严肃游戏的感染力，更好地体现寓教于乐。

Serious games are a new development direction of computer games. They can simulate interactive professional teaching environment and have been widely used in many fields, such as science education, rehabilitation, emergency management, and military training. Serious medical rehabilitation games are mainly used for medical technology training and rehabilitation-assisted treatment. They can train and improve the professional skills of medical staff, reduce the pain and boredom of patients during rehabilitation, and assist patients in rehabilitation treatment. Serious games in military training are mainly used in military modeling and simulation and possess controllability, security, and low cost. Virtual characters are simulated entities with life characteristics for serious games. They have credible behavior and can improve users' experience in serious games. At present, graphics rendering in serious games has gradually matured, but the research on virtual character behavior modeling is only in its first stage. A credible virtual character should have perception, emotion, and behavior. It can respond to the user's operation in time and has a certain reasoning ability. Modeling the behavior of virtual characters requires the knowledge of psychology, cognitive science, and specific domain knowledge. This paper aims to present a control algorithm that reflects the behavior of a virtual character under certain circumstances. This algorithm is an interdisciplinary application, which involves computer graphics, human-computer interaction, and artificial intelligence technologies. This paper summarized the existing studies on virtual character's behavior modeling from four aspects, namely, game plot and behavior, behavior modeling method, behavior learning, and behavior modeling evaluation. In the aspect of game plots and behavior, the design of behavior should contain the plot. The behavior of virtual characters accordingly change with the change in the plot. This condition was illustrated by the virtual character behavior design in the rehabilitation and military training plots. In the aspect of behavior modeling, the behavior modeling methods of virtual characters were summarized. The characteristics of finite state machines and behavior trees were analyzed, the behavioral learning methods were compared, the key elements of reinforcement learning were indicated, and the application of deep reinforcement learning was discussed. Reinforcement learning has four elements, namely, environment, state, action, and reward. Virtual character behavior decision learning could be completed by constantly attempting to obtain environmental rewards. In the aspect of behavior modeling evaluation, three indexes were summarized to evaluate the effectiveness of the model, namely, the real-time behavior of virtual character, the emotion-integrated behavior, and the behavior interactivity. An extremely slow character behavior response will reduce the user's interest in participating in the game, and a timely response will provide the user an efficient and pleasant experience. Users aim to achieve emotional communication with virtual characters in a virtual environment to have a good sense of immersion. A virtual character behavior framework was summarized on the basis of existing studies. It included four modules, namely, sensory input, perception analysis, behavior decision making, and action. Emotional factors are valuable to create virtual characters with credible behavior and realistic movements. They could also increase the appeal of the game. Issues that need additional research were discussed from the perspective of affective computing intervention, game story and scene design, smart phone platform, and multichannel interaction. Virtual characters should be introduced to expand the game plot and assist in teaching to completely realize the function of serious games. Serious games are different from movies. Users do not passively accept, and they learn through constant interaction. A virtual scene without any plot and any virtual character is difficult to attract users. A narrative plot can make it easy to learn. Virtual characters with behavior and emotional expressiveness can enhance users' emotional experience and guide users to learn in a real-life-like situation. The popularity of mobile terminals provides various applications for serious games and attracts many users to use serious games. Multimodel interaction would be popular in the future because single-model interaction will limit user's interaction with the virtual character. A multichannel interaction method could improve the intelligence of virtual characters and could be realized with visual, auditory, tactile, and somatosensory models. The behavior modeling of virtual characters requires comprehensive consideration of game plots, machine learning, and human-computer interaction technologies. Rigid behaviors could not attract users. Building virtual models with autonomous perception, emotion, behavior, learning ability, and multimodel interaction could immensely enhance user's immersion. These models are the development direction of serious games. Serious games provide an intuitive means for education and training. The behavior modeling of virtual characters is a developing core technology of serious games. At present, many problems need to be urgently solved. Affective computing methods, game plots, smartphone operating platforms, and multimodel human-computer interaction should be considered to improve the behavior model of virtual characters. The integration of interdisciplinary knowledge is required to create behavioral credibility, autonomous emotional expression, and convenient interactive virtual characters. These characters could provide a better learning experience for users and are easy to be promoted.