The invention relates to a lamp dimming circuit with electricity leakage preventing function, includes a power module, a PWM signal conversion module, an optocoupler, an analog signal conversion module, and a controller and a voltage conversion module for connecting the illuminator. By adding the PWM signal conversion module, optocoupler and analog signal conversion module, the external dimming input signals in turn converted into PWM modulation signal, optical signal and analog voltage signal, and transferring the converted analog voltage signal to the controller for processing, and the controller sends the processed signal to the voltage conversion module for processing. Since the voltage signal entering the optocoupler is transmitted in the form of light, and there is no Y capacitor crossover between the power line and the dimming line.