The invention discloses a human body activity posture monitoring method and system and a human body posture monitor, wherein the method comprises the following steps: receiving a microwave detection signal, wherein the microwave detection signal is a detection signal obtained after performing microwave scanning on a target area; according to the microwave detection signal, judging whether the current activity posture of a preset human body in the target area is in a dangerous posture range, wherein the current activity posture is the action form of the human body at a position at the current time point; and when the current activity posture of the preset human body in the target area is in the dangerous posture range, sending out an alarm signal. According to the human body activity posture monitoring method and system and the human body posture monitor in the invention, the technical problem whether a user is in a dangerous state cannot be determined due to the fact that the activityenvironment with large fog concentration cannot be monitored in the related art is solved.