Aim at the problem of traction motor minimum energy consumption for metro vehicle, a field current given strategy based on maximum torque per ampere control target was proposed, which could make the motor operate at constant torque range, constant power range and constant voltage range smoothly and effectively. According to the traction characteristics curve under different speed of the motor, and considering the max voltage and current limitation and the field current influencing on mutual inductance, the optimized given field current control was designed, which could obtained the same torque performance with the minimum motor current and improve motor efficiency. Simulation and experiment showed that the motor could operate at the whole speed range stably, practical current of which was lower than the designed.