Based on the original cooling system,an additional heat exchanger was added to solve the problem that the diesel locomotives cooling system cannot spread out enough heat amount under special conditions.By calculation and analysis,the optimal parameters of the additional heat exchanger satisfying the requirement of heat transfer ability and spatial sizes were provided.To ensure the stability of water inlet temperature of combustion engine,the needed water inlet flow of the additional heat exchanger was analyzed to match the water outlet temperature of the main heat exchanger.The new system can automatically control water flow according to the water inlet temperature of additional heat exchanger by using a thermostatic valve with linear characteristics to ensure diesel locomotive running safely and smoothly.