The invention discloses an illumination controlling circuit coupled between a household electricity input and an illumination lamp. The illumination controlling circuit includes a dimmer module, a sampling-and-holding circuit, a differential circuit, an integrator circuit and a clamping circuit. The dimmer circuit is used for generating a dimming signal which includes a plurality of waveform pulses. The sampling-and-holding circuit samples from the dimming signal, so as to obtain an average waveform pulse. The differential circuit is used for extracting a voltage difference of the average waveform pulse. The integrator circuit performs integration on the average waveform pulse according to the voltage difference, so as to generate a direct current voltage signal. When a level of the direct current voltage signal exceeds a threshold voltage level of the clamping circuit, the direct current voltage signal is used for driving the illumination lamp.