A dimming control method and a dimming circuit are used to control the brightness of a LED. The dimming circuit includes a power conversion unit having an input end, an output end, an inductor, and a switch. When the dimming current signal is higher than or equal to a first current threshold, the switch is controlled such that the power conversion unit operates in a continuous Conduction mode or a boundary Conduction mode; when the dimming current signal is lower than the first current threshold, the switch is controlled such that the power conversion unit operates in a discontinuous Conduction mode; and when the dimming current signal is lower than a second current threshold, the switch is controlled such that the power conversion unit operates in a chopping control mode.