Abstract To make the BSPWM-control inverter be of a good sine wave output, its output voltage harmonic is analyzed. It shows that the strongest harmonic is N order, and its amplitude is greater than fundamental under M<0.9. In order to eliminate furthest the high frequency harmonics and retain fundamental wave as much as possible, which will minimize the THD of output voltage, a passive filter circuit was put forward, and an estimating method for the filter component parameter was given. The theoretical analyses and calculated shows that the L-C filter will be little or no attenuation for fundamental wave and be a great extent attenuation for high-. The loss of the filter component gives influence so little as to be ignored, and the utilization coefficient can be maximized. The example shows that the THD is far less than 1%, and the filtration network is superior and efficacious.