This paper presents an equivalent magnetic circuit model to predict the leakage effect, especially the end leakage effect, of surface-mounted permanent magnet synchronous machine (SPMSM) in rim-driven marine current power (RMCP) system. The end leakage effect is usually neglected in most conventional permanent magnet (PM) machines. However, it is significant in the electrical generator of RPCM due to the short axial length. The idealized path and analytical expressions of end leakage-permeance are given in this paper. Finite Element Method (FEM) 3D/2D values are presented to validate the proposed analytical model. With no need for the time-consuming FEM-3D calculation, a correction factor base on the analytical mode is proposed to adjust the results (e.g. back-EMF, torque) of conventional design when end leakage is ignored in the calculation. The calculation results and experimental dines show that the proposed analytical model is accurate to analyze the leakage effects of SPMSM in RMCP system.