Abstract: As an important visual feature of trees,shadows are very important for keeping the visual fidelity of the rendering result,and the shadow rendering speed affects the whole scene's rendering speed significantly as well.A tree shadow generation and rendering algorithm is proposed in this paper,which especially fits to the widely used Billboard Cloud tree model.Based on Shadow Map,the algorithm uses a depth transformation method to solve the self-occlusion problem of Billboards,and uses shadow map filtering together with screen shadow map filtering to render the soft shadow of trees.Besides,the graphics hardware function,i.e.Multi Render Target(MRT),is used to optimize our algorithmic procedure.Finally,the algorithm is tested by a tree model from SpeedTree,and the experimental results have shown that the shadow of Billboard Cloud tree model generated by our algorithm has good view fidelity and the algorithm is of high efficiency.