This paper is based on a three-phase diode rectifier-fed motor drive system with small dc-link capacitor. To reduce the grid current harmonics of this system, a grid current control method is proposed. Considering the maximum conduction angle limitation of the rectifier diodes, the proposed method shapes the grid current into a square wave by adjusting the dc-link current of the motor inverter. Since the square wave has relatively few harmonics, the grid current quality can be improved. The proposed method has the advantage of requiring no motor parameters. Moreover, different from most of previous methods, the proposed method does not depend on additional circuits. The simulation results demonstrate that the proposed method is feasible.