As an energy-saving driving circuit widely used at present, frequency conversion device has been widely used in industrial field, especially in machine tool and robot control, because of its good speed regulation performance. Frequency converter is composed of non-linear switching semiconductor elements, which cause multiple harmonics in the output current, while conventional converters do not suppress harmonics. A method of injecting high-order harmonic compensation signal into SPWM sinusoidal signal was proposed to suppress specific sub-harmonics. The MATLAB/Simulink simulation and experiment show that the proposed method can be used to effectively reduce the specific sub-harmonics, reduce the harmonic distortion rate and improve the output current power quality.