Muscle fatigue is a common phenomenon in life and work, which reduces work efficiency and quality of life, and also affects the performance of the biomechanical interface. It is of great research value to collect and analyze the information related to muscle contraction to study the mechanism of muscle fatigue. In order to better study the athlete muscle contraction movement, the principle of photoelectric volumetric tracing (PPG) to detect the athlete muscle contraction movement is introduced, and a reflective photoelectric muscle contraction sensing system that can detect four signals at the same time is designed. A programmable constant-current source is used to drive an infrared LED to irradiate infrared light into the muscle tissue, and the light transmitted out of the muscle is detected by another infrared detection circuit and converted into an electrical signal. Under the control of the microcontroller, the four detected electrical signals are time-conducted by analog multi-switches, followed by low-pass filtering and AD sampling, and finally the obtained four data are transmitted to the upper computer through the Bluetooth module for subsequent processing. The circuit realizes the synchronous detection function of 4-channel signals, and the system is accurate, reliable and has certain practical value.