In order to study the influence of different cooling mediums on the fluid velocity and the temperature distribution of end parts in the turbogenerator end region, a 330-MW turbogenerator is analyzed. Three-dimensional fluid-thermal coupling analysis model of the turbogenerator end region is given. When the different cooling mediums are used, fluid velocity of fan inlet and pressure values of end-region outlet from the flow network calculation are applied to the end region as boundary conditions, and the losses from 3-D transient electromagnetic field calculation are applied to the end parts as heat sources in the fluid-thermal coupling field. The fluid field and temperature field in the turbogenerator end region are calculated using the hydrogen and air as cooling medium, respectively. Fluid velocity and temperature of end parts in the turbogenerator end region are compared when the different cooling mediums are used. When the hydrogen is used as the cooling medium, comparing the calculated temperature results with the test values, the calculated temperature results match well with test values. These will provide a reference for the ventilation cooling design of large turbogenerator.