A kind of human body image privacy protection algorithm was proposed for active millimeter-wave imaging security systems, the imaging effect of which was not affected by the height and the standing posture. The background noise of the millimeter-wave image was decreased and the edge details were increased by pretreatment of human body image. The morphological processing and binarization were used to distinguish human body image from background. The pixel traversal method and human body proportion determination method were initially used to locate the private parts of human body with standard posture. Subsequently, the calibration algorithm was used to locate the privacy parts of human body with different height and non-standard posture and thus improved the identity rate of location. Finally, the already positioned privacy parts were blurred to protect the privacy of people under inspection. The algorithm has been applied to the actual imaging products. Compared with the conventional ones, the proposed algorithm has high portability, fast running speed and high positioning accuracy.