A space vector pulse width modulation with a non-sinusoidal power supply (NSVPWM) is proposed to improve the stator iron utilization in a multiphase motor. When compared with three phase motors, there are more control freedoms in multiphase motors. The space vector distribution under a non-sinusoidal power supply is analyzed to achieve an optimized selection. Then the harmonic injection proportional coefficient is derived aiming at flux density optimization, which includes the air-gap and the yoke flux distribution. 15 kW and 630 kW nine-phase concentrated winding induction motors are used as practical examples. By maintaining the amplitudes of the air-gap flux density and the yoke flux density as well as the stator copper loss, the electromagnetic torque densities are compared under various load conditions. Experimental results show that when compared with the traditional sinusoidal method, the output torque is improved by 5.45% with the proposed NSVPWM method.