This paper proposes a method based on improved SSDA waveform matching to forecast the zero-crossing point of primary current and to increase the output power of high-frequency power supply by controlling the opening and shut-off of high frequency source control circuit. First considering the noise in waveform sampling process a waveform database was established through the sampling low-pass filtering and arithmetic median filtering of primary current under different conditions.Then by using the improved SSDA waveform matching and according to the waveform in the database the zero-crossing of the target waveform was predicted to control the power switch.The experimental result showed that the method proposed here is feasible with high matching speed and matching precision.