The large power mining dump truck usually has electric drive system for the harsh operating conditions of mining. The traction motor and multi-stage reducer are assembled in the limited space of the two rear wheels. The permanent magnet motor is often used as traction motor for its much advantage characteristic. However, the permanent magnet is particularly sensitive to the high temperatures since it can loose a part of magnetization when it is exposed to a high temperature. It is necessary to have better cooling system for improvement thermal performance of permanent magnet (PM) motor. The heat losses generated by permanent magnet motor in the off-road electric driving truck are cooled by the water to maintain the motor working effectively. This paper is focus on analyzing the thermal behavior of the PM motor numerically and experimentally. The 2-D transient temperature field of motor is investigated based on different losses of the permanent magnet motor which is determined by the magnetic field analysis. The water cooling housings with different channel layout are compared with the synthetic evaluation index which reflecting the comprehensive efficiency of cooling system. The 3-D CFD model of water cooling housing is developed to present the velocity and temperature field of the cooling water flowing in the circumferential channel. The temperatures of different part of PM motor with water-cooling housing are measured under different operating conditions. The experimental results show the validation and effectiveness of the simulation model in predicting thermal characteristics of the traction motor.