The traditional calibration method of transformer on-load tap-changer tester has difficulties in synchronous calibration of transition resistance, transition time and synchronization. In this paper, three variable resistor modules based on FPGA control DAC are designed to simulate different resistors. After frequency compensation, the variable resistor module can realize the rapid switching of resistors, a6nd realize the synchronous verification of analog transition resistance, transition time and synchronization. At the same time, the protection circuits of overvoltage, overcurrent and antireverse connection are designed to improve the reliability of the whole device. After testing, the maximum allowable error of transition resistance simulated by the calibration device is better than ±(0.2% RD+5 mΩ), and the absolute error of transition time and synchronization is less than 10 μs, which fully meets the needs of laboratory calibration and solves the calibration problem of transformer on-load tap-changer tester.