Abstract: Variable leakage flux permanent magnet synchronous motor (VLF-PMSM) suffers from the deteriorated performance in sensorless control system due to its characteristics of the inductance parameter mismatch and back electromotive force harmonics caused by novel leakage flux branches. To overcome the problem mentioned above, an adaptive decoupling robust position estimator was proposed for the VLF-PMSM sensorless control system. First, the proposed method simplified the VLF-PMSM mathematical model and reduced the effect of inductance parameter variations according to the active flux concept. Then, the robust and gradient descent algorithm was utilized to maintain the robustness to inductance parameter variations and eliminate the specific order harmonics caused by the novel leakage flux branches. Meanwhile, the accuracy and stability were enhanced. Finally, the feasibility of the proposed estimated system was verified.