Photorealistic rendering of rain streaks is a challenging task. A falling raindrop has complex optic effects due to its rapid oscillation and the reflections & refractions of a ray in itself. Furthermore

it is perceived as a motion-blurred rain streak observed by a human or a camera. In this paper

we present a Monte Carlo ray-tracing based approach to render photorealistic rain streaks. An acceleration structure is built in advance for the triangle mesh of a raindrop at every discrete time point in its oscillation period and an intersection computing is made between its motion bounding box and the sampled ray

which make a large acceleration to the ray-raindrop intersection test. An adaptive sampling technique

which avoids many samples for every pixel

is used to improve the sampling efficiency and to accelerate the image rendering. We integrate the approach into the off-line renderer(PBRT) and produce photorealistic images of rain streaks and rain scene animation. Experimental results show that our approach can be used to correctly simulate the reflections and refractions of a ray in a raindrop and efficiently render photorealistic rain streaks in the scene with any type of light source.