Abstract: A three dimensional numerical model of electric cabinet cooling system of HXD1 electric locomotive has been established and has done numerical simulation, getting velocity field and temperature field of its cooling system through calculation. The comparison with experimental results proved the rationality of its design. We also compared heat dissipation performance of the system under condition of different fans and different heat source positions, obtaining that collocation of fans is decisive in forced-air cooling flow field, and the rise of the speed of fans can improve heat dissipating efficiency, which will go down with the increase of power. We also found that reasonable heat source positions can optimize flow field and improve heat dissipation performance.