The high-power nonlinear load of the marine electric propulsion system will generate significant harmonic currents and cause grid voltage waveform distortion. The Electrical Transient Analyzer Program (ETAP) is used to establish the simulation model of the electric propulsion system of a survey ship, and perform the harmonic analysis and calculation. The simulation results show that the total harmonic distortion rates of the voltage are all within the specified range for the ship under various typical operating conditions. It can provide references for the harmonic processing of similar ships in the future.