The invention provides a method and system for calculating a passenger crowdedness degree, comprising steps of establishing a video data collection environment, collecting video data of passengers getting on and off, reading collected video data of passengers getting on and off, performing continuous multi-frame pre-processing on the video data, identifying people heads according to the pre-processing result, taking the detected human head as a target object to be tracked by mean value drift, determining the behaviors of getting on and off of the passengers in the area where the target object is positioned and determining the crowdedness degree of the passengers inside the vehicle according to the numbers of the passengers getting on and off. The invention also provides a system for calculating the passenger crowdedness degree. The technical scheme of the invention adopts the pre-processing which can eliminate the static background to overcome the interference on the identification of the head top of the people in the frame image which is caused by the change of the light, and can effectively reduce the false detection, leak detection and mistake detection through limiting the size of the detection window.