Abstract: Insulated Gate Bipolar Transistor (IGBT) module is the main heat source in the electric motor controller. To make the IGBT module work in a safe temperature range, a water-cooled radiator for a 45kW permanent magnet synchronous motor (PMSM) controller of electric vehicle was designed based on orthogonal experiment . Based on estimating the heat loss of the IGBT module, the radiator structure was determined preliminarily. The main factors affecting the performance of the radiator were clarified via thermal simulation. Then, the factors such as coolant flow rate, fin height, fin thickness, fin spacing, spoiler type and radiator substrate thickness were optimized by orthogonal experiment, and the optimal control and structural parameters of the radiator were obtained. Simulation results show that the designed radiator can meet the heat dissipation requirements of IGBT module.