The invention provides a behavior detection and identification method and system, and belongs to the technical field of computer vision. The method comprises the steps: obtaining a binary difference image sequence of a behavior video stream, calculating a middle mass center movement speed, a left mass center movement speed and a right mass center movement speed of each frame of image, comparing with a preset speed threshold value; if one or more of the three mass center movement speeds are greater than a speed threshold value, judging that the behavior in the image is overspeed, otherwise, judging that the behavior is not overspeed; counting the behavior overspeed times in unit time, if the overspeed times are larger than a preset overspeed times threshold value, judging that a violent limb behavior is detected, and giving an alarm, and otherwise, clearing away the recorded overspeed times, and starting a new statistical period. According to the invention, the movement speeds of a middle mass center, a left mass center and a right mass center are calculated, the algorithm is simple, the three mass centers have good complementarity, severe limb behaviors can be detected, missing detection and false detection are prevented, the detection reliability is improved, high-performance parallel computing equipment does not need to be arranged, and the cost performance is high.