Abstract: To achieve high reliability and performance of real-time collision detection in dynamic visualization of complicated 3D city models,the capsule primitive is defined to model the viewpoint's moving 3D space,and a two-step collision detection algorithm based on the capsule is proposed.This algorithm concerns with both the advantages of discrete and continuous detections,in which the first step of pre-detection significantly increases the computational efficiency,while the second step of intensive detection potently ensures the detection precision.The experimental result shows that the proposed algorithm is effective.