The invention discloses an open-circuit fault diagnosis method for the drive system of a double-winding fault-tolerant permanent-magnet motor. According to the method, the collected phase current of a motor is respectively subjected to the converting and processing process by a low-pass filter, a Clarke convertor, a Park vector processor, a normalization processor, an average value calculator, an absolute value calculator and an absolute value averaging processor, so as to obtain the average value of the normalized phase current of the motor and the average value of the absolute value of the normalized phase current of the motor. With the average value of the normalized phase current of the motor and the average value of the absolute value of the normalized phase current of the motor as a basis, fault diagnostic variables for the system are constructed, so that the open-circuit fault of the drive system of the double-winding fault-tolerant permanent-magnet motor can be detected and positioned in real time. Based on the above method, no extra current sensor is required, so that the method is simple, feasible and high in reliability. Based on the combined utilization of the average value of the normalized current and the average value of the absolute value of the normalized current, the incorrect diagnosis caused by load sudden change and other reasons during the conventional diagnosis process can be avoided. Meanwhile, the diagnosis time is greatly reduced. Therefore, the open-circuit fault of the drive system can be effectively detected and positioned in real time.