Abstract: In the electrified section, the cab signal equipment is often disturbed by the harmonic of the unbalanced traction current. In view of the shortcomings of low efficiency and large error in traditional cab signal anti harmonic interference test, an anti-harmonic interference testing system for cab signal equipment based on virtual instrument technology was designed. The system used PID control and established semi physical semi simulation environment of cab signal system to implement automatic testing of cab signal equipment against harmonic current interference. The system was programmed by LabVIEW platform, with simple development and good human-machine interface. The test results show that the efficiency and accuracy of the cab signal against harmonic interference have been significantly improved by using the system.