A set of high-precision friction stir welding force monitoring system was designed. The system’s main hardwares were strain force sensor, data acquisition card and computer. On this basis, the welding force monitoring system software was developed combined with signal processing methods based on LabVIEW virtual instrument technology, and the experiments of monitoring welding force was done. The system’s functions included multi-channel data acquisition, data processing, real time display and data storage. The overall structure of this system and system’s software and signal processing method were described in detailed. Finally, the accuracy and reliability of the system were verified by welding experiments. It provides a support of engineering experiments for optimizing welding process and improving the quality of welding.