A dimming controlling circuit for LED includes: a switch configured to connect a main circuit and a power grid; a switch-on duration controlling circuit configured to output a switch-on duration controlling signals according to action times of the switch; a switch-off controlling circuit configured to output a switch-off controlling signal according to a comparison result of the voltages of the switch-on duration controlling signal and of a signal from a terminal of a switch transistor in the main circuit; a switch-on controlling circuit configured to generate a switch-on controlling signal after a first preset duration since receiving the switch-off controlling signal; and a logic unit configured to output a switch transistor controlling signal.