The invention discloses a hydraulic intelligent circulation test system of a speed reducer and a test method thereof. The hydraulic intelligent circulation test system of the speed reducer comprises acircuit breaker, a contactor, a thermal relay, a hydraulic motor, a hydraulic clamping electromagnetic valve and a hydraulic opening electromagnetic valve, wherein the circuit breaker, the contactor,the thermal relay and the hydraulic motor are connected in series; the breaker, the hydraulic clamping electromagnetic valve and the hydraulic opening electromagnetic valve are connected with a hydraulic circuit correspondingly; a contact coil is arranged on the contactor, a relay switch is arranged on the thermal relay, and the relay switch is connected with the hydraulic circuit through the contact coil; the hydraulic intelligent circulation test system of the speed reducer further comprises a programmable controller which is used for writing a circulation test program, and an output wiringbar and an input wiring bar are arranged on the programmable controller; and the hydraulic clamping electromagnetic valve, the hydraulic opening electromagnetic valve and the relay switch are connected with a corresponding output contact on the programmable controller correspondingly, and an input contact for testing in the input wiring bar is connected with the hydraulic circuit through test buttons. According to the system and the method, the structure is simple and reasonable, the labor cost is low, the testing efficiency is improved, and the operation mode is flexible.