[Objective] To address the issue that traditional sensorless algorithms can only observe electrical angles and thus cannot be applied to servo positioning, this paper proposes an 8-pole, 9-slot interior permanent magnet synchronous motor with an asymmetric rotor. The asymmetric inductance characteristics of the rotor are utilized to observe its mechanical angle. [Methods] By introducing magnetic barriers and magnetic bridges with different parameters under different pole pairs of the rotor, the magnetic resistance of the main and leakage magnetic circuits between the stator and rotor was altered, leading to periodic variations in the inductance waveforms that were directly related to the rotor's mechanical angle. Based on the analysis of the magnetic circuit, a correction coefficient that considered the asymmetry of the rotor was introduced to modify the inductance calculation method using the winding function method. [Results] The results indicated that increasing the width of the magnetic barrier reduced the inductance, while increasing the height of the magnetic bridge increased the inductance. Compared to finite element simulation results, the average percentage error was approximately 1.59%. [Conclusion] The calculation and simulation results validate the feasibility of the proposed asymmetric rotor topology for identifying the mechanical angle in sensorless algorithm.