In order to study the fluid flow and heat transfer characteristics in a megawatt wind power generator, based on the basic principles of computational fluid dynamics (CFD) and numerical heat transfer (NHT), the finite volume method is used to model the generator, and the flow and temperature fields are calculated numerically. The correctness and accuracy of the calculation method are verified by comparing the calculation results with the experimental data. The temperature field of the internal flow field of the generator is analyzed, and the flow characteristics of the cooling medium of the megawatt wind power generator are revealed. Based on the analysis, the generator ventilation duct layout scheme is optimized, effectively reducing the temperature rise at the generator hot spots.