A generator design method which is the combination of electromagnetic simulation based on equivalent magnetic-circuit method using ANSYS Maxwell 2D and engineering thermal analysis is presented. Through the analysis and calculation by ANSYS Maxwell 2D, the 4.8 MW medium-speed permanent magnet wind power generator is designed. In order to further study the operation characteristics of the generator, the finite element analysis and calculation model of the permanent magnet generator is established. The no-load, rated-load and short-circuit performances of the generator are simulated, and the current, induced voltage and electromagnetic torque are obtained. Finally, the temperature rise of each part of the generator is calculated by the thermal circuit method. The calculation results show that the design of the generator is reasonable and all indexes meet the requirements. The combination of electromagnetic simulation and engineering thermal analysis can make the generator design more accurately. It provides the theoretical basis for the electromagnetic design and structural optimization of generators.