Abstract: An accurate collision detection algorithm considering tolerance information is proposed to solve the problem of low accuracy in collision detection due to polygonal models in virtual assembly currently.The algorithm mainly consists of the following four parts:first,hierarchical collision detection of polygonal models is carried out to obtain collided polygons;second,collided polygons are mapped to geometries using hierarchical image data;third,collision threshold is computed based on tolerance of geometries;fourth,accurate collision detection is carried out based on collision thresholds.Experiments show that this algorithm provides more accurate result than common algorithms and meets the real time requirement of virtual assembly at the same time.