A thin photoelectric mechanical keyboard switch includes a printed circuit board (PCB), a base, and a keycap. A first accommodation slot, a second accommodation slot, and a surrounding slot are provided at the base. A balancing frame is disposed in the surrounding slot. A torsion spring is arranged in the first accommodation slot. An upper through hole is provided at a bottom portion of the second accommodation slot, and a blocking piece, a hanging piece, a tension spring, and a guiding core are disposed in the second accommodation slot. One end of the tension spring is fastened in the guiding core and connected to the hanging piece, and the other end of the tension spring is connected to the balancing frame. The thin photoelectric mechanical keyboard switch utilizes light to implement turning on and off functions, realizing a thinned design, and enhancing pressing balance performance and stability.