Based on the whine noise problem of the electric bus gearbox, the electric drive system of a certain electric bus was taken as the research object. A rigid flexible coupling dynamic model of the “gear box-motor rotor” was established. The orthogonal ex- periment method was used to analyze the influence of the gear modification parameters on the transmission error, and studiedon the gear modification theoretical principles. The boundary element method was used to establish the prediction model of the radiated noise of the gearbox, the optimization scheme was evaluated according to the noise simulation results. Finally, the feasibility of the modification scheme was verified by the bench test. The experiment results showed that the gearbox noise problem had been improved significantly, and the optimal design method of the electric bus gearbox low noise based on the gear modification was established.