A car light module junction unit is provided to weld light modules made of the different material by controlling the intensity of the laser. A car light module junction unit comprises: a power unit(216) provided with the external power; a robot knuckle unit(210) in which several arms are connected based on an axis of rotation and an end part moves the three dimensional space; a driving unit(212) receiving the electrical energy applied in the power to move the robot knuckle unit; a laser head(200) changing the electrical energy applied in the power to laser; a connecting member(202) connected in the end part of the robot knuckle unit; a ball(204) inserted in a groove in order to slide and rotate; and controller(214) controlling the driving unit. The ball is moved with the controller according to a part where a first member and a second member are overlapped.