A new method for subcutaneous fat thickness detection based on ultrasound RF echo distribution is presented. Firstly, this method analysis superficial tissue structure characteristics, and find out the different signal features of the tissue from the RF echo signal. Secondly, the thickness of each tissue layer is detected by pulse echo method. Then the results are compared with B mode ultrasonography and straightedge. Finally, the threshold is set for peak detection of 〖HJ*4/9〗RF echo signals. The results of experiments indicate the feasibility of detecting the subcutaneous fat thickness by ultrasound RF echo signals.