During the design and finalization process of an urban rail vehicle, the condensing fan was sheltered due to the limitation of the overall arrangement. In order to evaluate the influence of the shielding on the heat dissipation capacity of the whole cooling loop, the potential risk of the motor cooling system is evaluated with the help of 3D simulation method based on STAR CCM+ combined with a variety of 1D verification methods. When the current overall arrangement has an impact of 11.4% on the air intake of the condensing fan, after checking and analyzing the potential risk of the motor cooling system, it is found that the radiator still has sufficient margin and the risk is controllable. Based on this, an evaluation method for the working condition of the motor cooling system is developed.