In a single-live-wire dimming circuit for an LED lamp, a brightness wall controlling unit supplies electric power to a brightness adjustment driving unit in a single-live-wire manner. The brightness adjustment driving unit drives an LED lamp. The brightness wall controlling unit is composed of a single-live-wire power supply module, a rectifying phase-shift driving module, a waveform sampling and shaping module, a single-chip microcomputer control module, a triggering control module and a brightness setting module. The brightness adjustment driving unit is composed of a single-phase rectifying and voltage-stabilizing module, a brightness signal receiving module and a brightness driving module. When the brightness changes, the brightness wall controlling unit transmits a brightness controlling signal through controlling the phase shift angle of a voltage waveform which is outputted by the single live wire. The brightness adjustment driving unit changes the brightness of the LED lamp according to the brightness grade in the brightness controlling signal. The LED lamp dimming circuit can be used for replacement and upgrading of a common illuminating lamp which is controlled by the wall controlling switch.