Flow network was built according to the ventilation structural characteristics of a 330 MW large water-hydrogen-hydrogen cooled turbogenerator. The variation of the fan inlet velocities, and the flow rates and pressures (boundary conditions) of each end region outlet were obtained, respectively, with different air gap spacer heights and different shelter board widths between the long press fingers by flow network method, and the relative law was analyzed. In order to study the influence of the changed end ventilation structures on the temperature distribution of the end parts, 3-D transient electromagnetic field in the turbogenerator end was calculated, and the eddy current losses (heat sources) of the end parts were gained by the finite-element method. Meanwhile, the fluid and thermal mathematics and physical models of the end region were given. Using the finite-volume method, the influence of the changed end ventilation structures on the surface heat transfer coefficient and the temperature of end parts was researched. It shows that the proper changes in the air gap spacer height and shelter board width decrease the copper shield temperature and result in a reasonable temperature distribution in the end parts. It provides the useful reference for the further design of the large turbogenerators.