The present invention relates to a control method for supporting active power factor correction (APFC) loads, comprising: providing square wave width of an output voltage waveform to be a comparatively large value to improve effective value of the output voltage, in order to meet the requirements for active power factor correction (APFC) loads; and gradually decreasing square wave width of the output voltage waveform from the comparatively large value to a comparatively small value to gradually decrease effective value of the output voltage to a desirable stable voltage effective value. The present invention further relates to a control system for supporting active power factor correction (APFC) loads, comprising: a voltage increasing unit for providing square wave width of an output voltage waveform to be a comparatively large value to improve effective value of the output voltage, in order to meet the requirements for active power factor correction (APFC) loads; and a voltage stabilizing unit for adjusting square wave width to a comparatively large value, and gradually decreasing square wave width of the output voltage waveform from the comparatively large value to a comparatively small value to gradually decrease effective value of the output voltage to a desirable stable voltage effective value.