Magnetic gears are a force transmitter consisting of permanent magnets. The mechanical input can be transmitted to an output shaft without contact by magnetic forces. The transmission property of the magnetic gears is usually better than that of mechanical gears, because it is free from transmission loss, mechanical friction, lubrication oil, dust, and ambient noise. However, in the analysis and experimental results is that there is a big difference has been reported. As one of the causes, in the analysis is considered that the actual movement of the magnetic gear has not been reproduced. Therefore, we have tried to do a detailed analysis of movement by calculating the torque from the results of magnetic field analysis. By solving the equations of motion from the torque applied to the secondary rotor, to calculate the position of the secondary rotor of next step, do the analysis in line with the actual movement of the magnetic gear. In this paper, we show the coupled analysis result of magnetic gear and effectiveness of 3D-BEM.