<p>This paper proposes a magnetic equivalent circuit based electromechanical modelling method for the propulsion shaft system driven by a permanent magnet synchronous motor. On the basis of the conventional magnetic equivalent circuit method, an improved air gap permeance calculation method is introduced to precisely quantify the air gap non-uniformity. Besides, the current vector control model based on Maximum Torque Per Ampere strategy and Space Vector Pulse Width Modulation-based inverter is established, and the effects of current harmonics can be efficiently considered. The differential equations of motion for the propulsion shaft system are derived, and the complete electromechanical dynamic model is finished. The proposed model achieves comparable accuracy to the finite element method and experimental results, and exhibits higher computation efficiency. Based on the propulsion shaft system electromechanical model, the effects of coil pitch on the permanent magnet synchronous motor flux linkage and vibration are analyzed. The coil pitches for low energy consumption and vibration permanent magnet synchronous motor are recommended.</p>