When the large-capacity turbine generator is operating, there is a large amount of copper and iron losses on the stator, which is seriously heated, may lead to local high temperature and even burn accidents. It seriously affects the safe of the generator. Therefore, this paper takes a 350 MW turbine generator cooled by water-hydrogen as an example to conduct thermal study on the key components of the stator. Firstly, the global fluid network model, the 2D electromagnetic field-path coupling model and the 3D half-tooth and half-groove full-axial fluid-structure interaction model of the stator is established based on the mathematical equations. Secondly, the inlet and outlet conditions of hydrogen and water, the heat flow density of each part are solved. The temperature of stator is calculated and measured to verify the correctness of the results. Then, the temperature distribution of key components such as cooling water, windings, and main insulation in the stator are studied. Finally, the multi-temperature peak-to-valley value of windings, and large multi-direction temperature difference of main insulation are described. The conclusion of this paper provides theoretical support for optimizing the temperature distribution of the stator and preventing the damage of the main insulation performance.