The invention relates to an electric power maintenance testing device, specifically relates to an ultra-high voltage circuit breaker closing resistance tester and solves a problem that the existing closing resistance testing device and method are complicated and time-consuming in operating process and easy to wear internal devices of a circuit breaker and aggravate the aging of components. The scheme is that the ultra-high voltage circuit breaker closing resistance tester comprises a current detection optocoupler, an anode of the current detection optocoupler is sequentially connected with a resistor and a power supply, a cathode of the current detection optocoupler serves as a measuring terminal, an emitting electrode of the current detection optocoupler is grounded, and a collecting electrode of the current detection optocoupler is connected with a second resistor, the power supply and a DSP (Digital Signal Processor). The power supply is an AC signal source with the output containing 10V DC bias after being amplified by a power amplifier, the peak of an AC signal component is 5V, and the frequency is 1kHz. The advantages are that 1, the testing device is simple in structure andlow in cost; 2, the testing method is simple and efficient to operate, and the measuring result is accurate; 3, the circuit breaker is not required to be disassembled, the internal devices of the circuit breaker are not worn, and the aging is not aggravated; 4, the input time of the circuit breaker can be measured at the same time; and 5, the ultra-high voltage circuit breaker closing resistance tester is very applicable to testing the closing resistance of 500kV and above ultra-high voltage circuit breakers.