The invention discloses a human body motion capture and posture analysis system and a method for carrying out foreground detection and automatic extraction of joint points through the human body motion capture and posture analysis system. According to the human body motion capture and posture analysis system, a human body motion image is captured through a camera, the human body foreground and the human body joint points are extracted from the human body motion image, and then human body motions are analyzed through a tracking and recognition algorithm. Due to the fact that a human body target in a video is extracted through an algorithm combining a background difference method and a frame difference method, the defect that background noise interference easily exists in the process of foreground detection based on the background difference method is overcome; due to the fact that the method with combination of a plurality of algorithms is adopted, automatic initialization of the human body joint points is achieved, and the defects that optical marks or manual marking is needed by a traditional joint point extraction method, and an existing automatic extraction method is large in calculated amount and poor in accuracy are overcome. The human body motion capture and posture analysis system is low in complexity and high in accuracy, and the intelligence and the efficiency of the human body motion capture and posture analysis system are improved.