The invention discloses a method for diagnosing open-circuit faults of a double-winding permanent magnet fault-tolerant motor drive system. In the method, the collected motor phase currents are respectively passed through a low-pass filter, a Clark transformation, a Park vector processor, a normalization processor, The conversion and processing of the average value calculator, absolute value calculator and absolute value averaging processor can 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, based on these two values The fault diagnosis variable of the system is constructed, so as to realize the real-time detection and location of the open-circuit fault of the double-winding permanent magnet fault-tolerant motor drive system. This method does not need to add an additional current sensor, is simple and easy to implement, and has high reliability. Through the joint use of the average value of the normalized current and the average value of its absolute value, it avoids the problems that are easily generated by conventional diagnostic methods due to load mutations and other reasons. Misdiagnosis, and the diagnosis time is also greatly shortened, which can effectively detect and locate the open circuit fault of the system in real time.