When the magnetic flux of a permanent magnet synchronous motor changes rapidly, it is approximately assumed that a magnetic flux change rate of 0 will constrain the performance of the PMSM fault-tolerant control system. This paper proposes a model free super twisting sliding mode composite fault-tolerant control method based on intelligent proportional integral differential (iPID-MFSTSMC). Firstly, a mathematical model for PMSM demagnetization fault was constructed, taking into account the variation of permanent magnet magnetic flux. Based on the constructed model, a magnetic flux sliding mode observer was designed to observe the magnetic flux and its rate of change. In addition, a load torque derivative sliding mode observer was designed for rapidly changing load torque. Then, an iPID model free fault-tolerant control method was designed based on observations of magnetic flux and its change rate, as well as load torque derivatives. The proposed control method uses a super twisting sliding mode algorithm to suppress observation errors and other disturbances, improve dynamic performance, and reduce the difficulty of controller parameter design. The stability of the designed fault-tolerant control method was proved using Lyapunov stability theorem, and parameter design conditions were provided. Finally, under the condition of rapid change of flux and load torque, simulation and experimental analysis show that the proposed method can effectively reduce the system jitter and reduce the overshoot.