A dimming system for LED lamps, comprising a DC/DC converter, a dimming signal input module, a brightness value conversion module electrically connected to the dimming signal input module, and a dimming signal switching threshold setting module, a first signal output module, and a second signal output module. The dimming signal input module is configured to input a dimming signal. And when the brightness value is greater than or equal to the dimming signal switching threshold, the value of the amplitude dimming voltage output by the first signal output module is equal to the dimming signal switching threshold and the second signal output module outputs one PWM signal. The PWM signal modulates the amplitude dimming voltage having a magnitude equal to the dimming signal switching threshold to adjust the output of the DC/DC converter.