The invention relates to a cooling system of a piston thermal fatigue simulation test bench and belongs to the test equipment technology field. The system comprises a fuel tank, a manual switch, a filter screen, an electromagnetic valve, an oil pump, a check valve, a temperature sensor, a flow sensor, a pressure sensor, a box body, an oil inlet pipeline, an oil collecting tank, a nozzle, a clamp,a piston, an oil return pipeline, the manual switch, the filter screen, a radiator and a temperature sensor. Cooling oil is adopted as a cooling medium. A new cooling medium different from the coolingmedium of a traditional piston thermal fatigue simulation test bench is adopted, a piston cooling environment can be fully simulated, a cooling speed is high, operation is easy, an application rangeis wide, working efficiency is high, and a research and development period is greatly shortened.