The present invention relates to a driving circuit and a driving method for LED. The driving circuit for LED comprises an inductor used for producing an output current, a power switch coupled to the inductor and used for controlling the inductor to transmit the output current to a plurality of LEDs and drive the plurality of LEDs, an adjusting circuit receiving a PWM signal related to the output current, and a driving unit producing an adjusting impedance value according to the PWM signal. The driving unit generates a switching signal according to the adjusting impedance value. The switching signal switches the power switch and enables the inductor to produce the output current. The driving unit adjusts the frequency of the switching signal according to the adjusting impedance value.