The articulated dump truck with independent suspensions is driven by six AC motors and each wheel is driven by one motor. Cooling system is configured in every electric wheel. The motor is the main heating source in the electric drive system. Hence, the cooling of the motor will affect the reliability and power-density of the whole electric drive system. According to the actual working conditions, the heating calculation about the cooling system has been carried out during the design process. The design concept of embedding spiral-shaped flow path in the shell of the stator has been drawn. The cooling water could pass through the path and accomplish cooling outside the stator. In this paper, the FLUENT has been used for the 3-D numerical simulation of the cooling system. The temperature field distributions of the cooling water and the shell are obtained. To analyze the influence of the shell structure on the cooling effect, the iSIGHT has been used to accomplish the structural and thermal optimization. The simulation and optimization results show that the cooling water velocity has little effect on the cooling, but the structure of the shell affects the cooling greatly. Finally, the section sizes of the shell flow path are optimized. As a result, the average temperature of the shell wall has reduced from 364K to 357K. The cooling effect can be improved significantly.