The invention relates to a single-fiber three-way multiplexer chip for fiber to the home, which is formed by an asymmetrical Y-branch waveguide and a multimode interference (MMI) coupler which are cascade-connected. An air slot is etched on the surface of the left branch of the asymmetrical Y-branch waveguide and is arranged between the core layer and the substrate of the left branch. The right branch of the asymmetrical Y-branch waveguide is a symmetrical waveguide. The invention has the advantages that the device structure is compact, kinds of optoelectronic integration can be realized, themass production can be realized and the cost is low.