A dimming control method and circuit thereof are provided. After receiving a TRIAC signal with at least one positive/negative half cycle waveforms, the turning points of the positive/negative half cycles are detected to obtain the conduction angles of the positive/negative half cycle waveforms. Then, a pulse width modulated signal with the symmetrical positive and negative half cycle waveforms is rebuilt to control a lamp. Therefore, the disclosure can solve the flickering issue of the lamp.