[Objective] In position servo applications of interior permanent magnet synchronous motor (IPMSM), accurate detection of the rotor’s initial position is essential for ensuring absolute position control precision. However, traditional sensorless control algorithms commonly face two limitations: the starting position is constrained to specific points, and mechanical angle deviation occurs during the pre-positioning process. [Methods] To address these issues, an initial mechanical angle identification strategy without pre-positioning was proposed for IPMSM. Firstly, the inductance mathematical model of the self-sensing topology IPMSM was established, and the mechanical fundamental frequency characteristics of the self-sensing IPMSM inductance were analyzed. Secondly, the mathematical model of high-frequency response current after line-to-line injection was derived, and the initial mechanical angle of the rotor was detected by utilizing the correlation between the high-frequency response current and the rotor’s initial mechanical angle. Finally, the proposed strategy was verified on a self-sensing IPMSM test platform. [Results] The experimental results demonstrated that, compared with the conventional strategy, the proposed control strategy achieved arbitrary position identification across four sectors without requiring multiple pre-positioning steps. [Conclusion] The proposed solution addresses the starting and pre-positioning travel limitations of traditional methods, providing a superior approach for pre-positioning-free startup of IPMSM.