This paper investigates a method to increase the energy economy of motors for an electric vehicle (EV) traction system. The low torque region of an EV motor is frequently used in everyday urban driving. Pulse-width modulation (PWM) carrier harmonic loss accounts for a high percentage of total loss for EV motors in this region. This paper reveals the relationship between fundamental and harmonic iron current for a permanent magnet synchronous motor (PMSM) by double Fourier integral analysis and builds the global loss model of PMSM which considers about both fundamental and harmonic loss. Based on the global loss model, an efficiency optimization control strategy is proposed in this paper, which can achieve the maximum efficiency by adjusting the flux-weakening current to the optimum value in the whole operation range for EV. Comparison among different control algorithms is drawn from both analytical and experimental results, from which the effectiveness of efficiency optimization control is verified.