The invention discloses an automatic assembling machine for a plug of an LED lamp. The automatic assembling machine comprises a base, a working disc, a position-selecting small disc, a discharging device, a riveting device, a copper needle assembling device, a black sheet assembling device, an internal insulation plate assembling device and a control box, the copper needle assembling device, the black sheet assembling device, the riveting device, the internal insulation plate assembling device and the discharging device are rotataby distributed on the periphery of the working disc in sequence,the position-selecting small disc is mounted at the position, located on one side of the working disc, of the base, an automatic grabbing device, a plug shell auxiliary positioning device and a plugshell feeding device are arranged on the periphery of the position-selecting small disc, and the automatic grabbing device, the plug shell auxiliary positioning device and the plug shell feeding device all adopt a cylinder to drive a mechanical arm so as to grab and move a shell of the plug. The position-selecting small disc is used to position the shell of the plug so that the shell of the plug is positioned well before entering he working disc, in the follow-up assembling process, the position of the shell of the plug is determined, the follow-up adjustment does not need, success assemblingcan be achieved with the error allowed, and the product pass rate is increased accordingly.