To mitigate the limitations associated with traditional direct torque control for permanent magnet synchronous motor (PMSM), which include variable switching frequencies, high torque ripple, and low power factor. This paper introduces a direct torque control strategy that utilizes a variable reference magnetic flux amplitude. Building upon the foundation of three-level voltage vector modulation for direct torque control, the strategy combines the idea of zero direct-axis current in vector control of PMSMs to establish a reference stator flux assignment policy. In order to solve the problem of inaccurate flux and torque estimation caused by the change of motor parameters during operation, an estimator based on model reference adaptive system was proposed. Simulation results demonstrate that this strategy exhibits excellent dynamic and steady-state response performance, has higher efficiency compared to traditional direct torque control, and effectively mitigates neutral point potential drift in three-level inverters. The simulation results validate the effectiveness of the proposed method.