The present disclosure provides a signal generating method and a circuit for controlling dimming of an LED. The method comprises generating a first pulse signal, the first pulse signal comprising information of P bits gray levels, P being an integer, wherein the minimum pulse-width of the first pulse is N, N is an integer; generating a second pulse signal after the first pulse signal, the second pulse signal comprising information of Q bits gray levels, Q being an integer, wherein the amplitude of the second pulse signal is different from the amplitude of the first pulse signal, the minimum pulse-width of the second pulse is the same as the minimum pulse-width of the first pulse; and utilizing the first pulse signal and the second pulse signal to represent gray levels information of the LED.