A system to gauge the strain between the prosthesis and the spacer in the medical operation of Total Knee Replacement (TKR) is proposed, with which the doctors can know the strain distribution in the knee and can make sure whether the strain is in balance. The load cells are used to gauge the strain, the micro CPU is used to control the system and process the figures, the wireless is used as the transmission way and the results are displayed visually and in real-time. The errors are analyzed theoretically, the test scheme and test results are given too and results are processed to improve the precision. The result shows the system has the features of efficiency, reliability, high precision, which verify the feasibility of the design.