Taking the motor controller of an electric counterweight forklift truck as the research object, the heat dissipation path and thermal resistance of the controller were analyzed theoretically. The simulation experiment was designed from two aspects of heat sink design parameters and fin types. The finite element thermodynamic simulation experiment was conducted by establishing a simulation model to explore its influence on the heat dissipation performance of the motor controller. The results show that the fin thickness, number and height of the heat sink have a great influence on the heat dissipation performance of the heat sink. Among the three commonly used fin types of heat sinks, the saw-tooth heat sink has the best heat dissipation. Combined with the simulation experiment, the design of the heat sink is optimized, and the optimized MOSFET junction temperature is reduced by 4.9981 ℃, and the optimization effect is obvious. Finally, the temperature field distribution of the heat sink was obtained by the infrared thermal imager in the real experiment, and compared with the simulation results which proved that the established simulation model is reliable.