The utility model provides a fault diagnosis device for ring main unit power distribution terminal. The fault diagnosis device comprises aviation plugs and a tester. The tester is at least configured to realize the following functions: according to the preset test scheme or test scheme input in real time, generating and outputting output voltages, output currents, state input signals simulating switch motion and state output signals simulating switch state, thereby enabling the output voltages, the output currents, the state input signals and the state output signals to be transmitted to the power distribution terminal; and realizing communication with the power distribution terminal through serial port lines or a network cable, so that by comparing the information received from the power distribution terminal with the information transmitted to the power distribution terminal, fault diagnosis can be obtained.