Two-dimensional animation is a labor-intensive process， where automatic keyframe in terpolation (inbetweening) is a research focus.Two-dimensional shape-blending plays a key role in keyframe inbetweening. Most of the existing 2D shape-blending algorithms are designed for a single closed polygon. When they are applied to complex shapes containing multiple regions， overlaps between different regions may occur. Our algorithm first obtains closed regions of input keyframes and calculates the matching relations between these regions. Then we iteratively construct a local coordinate system relative to its parent region for each child region. Then the hierarchical constraint relation can be used to get rid of “motion” mismatches between parent-child areas. Experimental results show that our algorithm can synthesize naturally smooth inbetweens and is efficient enough for practical demands.