Taking an asynchronous traction motor as an example, introduced the process and the principles of the motor cooling system design. Firstly, the improvement measures of the flow distribution were proposed based on analysis of the flow characteristics of the coolant in the motor. Secondly, the calculated value and the experimental value of the stator winding temperature rise were compared, and the results showed that the calculation method was feasible. Finally, the impact of altitude on the properties of air and the motor wingding temperature rise was analyzed, and the importance of considering the operating environment in the design of cooling system was emphasized. The design thinking and conclusions had certain referential value for the cooling design of asynchronous traction motor.