The paper introduces a variable frequency power on permanent magnetism step rotation pulse-width modulation. It consists rectifier filter, computer control circuit and inverter. According to the equal-acreage principle, the computed width data of the chopped pulse of the frequency conversing power gets two-phase data in 60°, and the output wave of this mode make the motor magnetism constant, while each magnetism directions on two sides of each chopped wave keep invariable, so the magnetism is regarded as step rotating in microcosmic. If theoretic output plus is 100% standard pulse-width modulated sine wave, the harmonic distortion can be less than 5%. When they are working, the wave is double polar in two-third cycle and single polar in one-third cycle in order to make total power wastage reduce by one-third. If depress the frequency and keep the pulse width, output voltage whose fall is in proportion to the frequency's fall can be got, so as to realize variable frequency, variable voltage in order to certain the output of the unsaturated motor magnetic circuit and constant torque. The power can be widely applied in the fields of machinery, metallurgy, chemical industry, light industry, etc.