A method and device for manufacturing low temperature poly-silicon, and a laser assembly are provided. A method for manufacturing low temperature poly-silicon includes forming an amorphous silicon layer on a substrate; controlling a relative movement of a laser assembly to the substrate in a direction perpendicular to a thickness of the substrate, and controlling a laser beam emitted from the laser assembly to irradiate the amorphous silicon layer on the substrate, to recrystallize an amorphous silicon in a region to be irradiated with the laser beam in the amorphous silicon layer. In a direction of the substrate moving relative to the laser assembly, energy of the laser beam emitted by the laser assembly in a same period of time decreases gradually.