The utility model relates to detection of faults of an on-load tap-changer of a transformer, and specifically relates to a fault simulation device for an on-load tap-changer of a transformer. The device comprises a relay, inductance coils, and a time control single-chip microcomputer. The relay has a contact K1, a contact K2, a contact K3, and a contact K4, and a tap switch which can be closely connected and cooperated with the contacts. The number of the inductance coils is two, wherein one inductance coil has a node 1, a node 3, a node 5, a node 7, and a node , and the other inductance coil has a node 2, a node 4, a node 6, a node 8, and a node 10. The device simulates transition conditions of different tap switches through changing values of resistance, and simulates spring aging or looseness fault conditions through changing switching time of the control relay, and simulates fault condition that a transition resistor of the tap switch breaks through disconnecting the resistor. The device can be connected with the inductance coils to simulate a real fault waveform of a field winding test.