To analyze the forced excitation capability of double water inner cooled condenser, three-dimensional numerical simulation was carried out to study the rotor winding temperature rise under forced excitation by using Fluent software. A three-dimensional model of the rotor winding was build according to its actual size, and the transient temperature distributions of cooper and water in the rotor winding under forced excitation by grids division and governing equations solution. Finally, the result was compared with that from the one-dimensional approximate calculation, the shortcomings of the traditional one-dimensional approximate calculation method were pointed out. The results show that the three-dimensional numerical simulation provides a higher accuracy. The research has an important guiding significance for the theoretical calculation of transient temperature rise and the design to the temperature margin in rotor winding of double water inner cooled condenser.