The invention relates to a large scale crowd video analysis system and a method thereof. The system comprises a crowd density calculation module, a crowd prospect segmentation module, a crowd tracking module, a crowd state analysis module and an event determination module. The crowd density calculation module, the crowd prospect segmentation module and the crowd tracking module process video image data and then the crowd number, a crowd area, a crowd motion direction and a speed are acquired respectively. The crowd state analysis module carries out processing analysis based on the acquired crowd number, the crowd area, the crowd motion direction and the speed and sends an analysis result to the event determination module. The event determination module is used for determining whether a crowd event is abnormal. The crowd event means that the crowd reaching a certain scale carries out one group characteristic behavior in a monitoring area. By using the system and the method, monitoring personnel can complete intelligent trend prediction, characteristic event positioning and other tasks; and effective help is provided for prevention of emergency, suspicious clue tracking and the like.