High-altitude electromagnetic pulse (HEMP) can produce electromagnetic interference (EMI) on the generator system. Without a precise machine model, over-voltage on the stator winding of generator cannot be accurately evaluated, and this is a new challenge for the design of nuclear power plant generator system. Therefore, the paper establishes the motor model by considering multi-conductor transmission line, and employs this model to design a set of precautions. At first, the expression of HEMP and coupling channel of HEMP are performed to analyze magnitude and waveform of over-voltage caused by HEMP. Then, a novel stator winding model is developed which bases on the analysis for multi-conductor transmission line. This model considers the influence of E1 on frequency-dependent parameters, and the voltage of winding per turn under HEMP can be calculated fast and accurately via it. The proposed approach can be validated through a three-dimensional electromagnetic simulation software based on the finite integration method. Finally, couple of precautions are derived based on the existing lightning protection measures and the above analysis.