Aiming at the fact that the circuit simulation and electromagnetic analysis method is difficult to accurately take into account the magnetic material permeability nonlinearity, and the finite element method is difficult to analyze the external circuit with non-standard sine excitation, we use the field-circuit coupling method to analyze the efficiency of in-wheel motor for electric vehicle, solve the electromagnetic field finite element equation and the external circuit equation together, and consider the influence of nonlinear factors such as time harmonic current on the magnetic field, to realize the direct coupling of the electromagnetic field quantity and the electrical quantity. The coupling equations of the electromagnetic field and the external circuit of the in-wheel motor, the equation of motion and the power loss are derived, and the load induced electromotive force and power loss are calculated, the difference between the finite element method and the field-circuit coupling method is compared, then the distribution of power loss density is studied. The efficiency characteristics of the motor under different working conditions are calculated by finite element method and the field-circuit coupling method respectively, and the results show that the field-circuit coupling method is more accurate and the correctness of the analysis method is proved.