Abstract: The simulation and analysis of human motion is a popular issue in simulation area and it is highly valued in sport motion training and analysis. Video is the main record form of athlete train. It is significant if we put the athlete motion of video and the normal motion of 3D virtual athlete of simulation system into the same screen because it is easy and accurate to compare the difference between them. And it will greatly benefit the athletes so that they can compare their motions with the normal motion of 3D virtual athlete and improve their competition level. While the motion of 3D virtual athlete can be observed from different viewpoints, the appearance will be different. So it is crucial to ensure that the viewpoint of virtual camera in simulation system and that in the video are the same. To solve the problem, a new concept of “virtual-real” comparison is put forward. Virtual here refers to the simulated motion and real is the sport video. The virtual-real comparison technique is to get the camera information from video and to adjust the view point of the virtual camera of 3D simulation system automatically. This technique is implemented in a trampoline sport simulation system and sound results are obtained. The use of virtual-real comparison technique extends the function of the sport simulation system and has greatly benefited the athlete in training.