The influence of permanent magnet motor stator slot width on electromagnetic noise was focused on. The relationship between electromagnetic force and the stator slot width was deduced by the analytical calculation of electromagnetic force. Electromagnetic field calculation was carried out for a permanent magnet motor for electric vehicle by Ansoft software, so as to solve the change of electromagnetic force wave with the change of stator slot width. At the same time, the 2D sound field of this permanent magnet motor was calculated by Ansys software for different slit widths. At last, experiment verification was performed. The simulation calculation result was basically identical with the experiment. This research could provide reference for weakening noise in motor designing process.