The invention discloses a horizontal on-load capacity-regulating tap switch which comprises a shell, a vacuum arc extinguishing assembly, a double-station switching assembly, a low-voltage contact assembly and a wiring assembly, the vacuum arc extinguishing assembly, the double-station switching assembly, the low-voltage contact assembly and the wiring assembly are fixed in the shell, the shell comprises an insulating substrate, and the wiring assembly is provided with a plurality of first wiring pieces. The wiring assembly is provided with a plurality of first wiring pieces, the first wiring pieces are in lap joint with taps on the high-voltage side of the transformer, the wiring assembly is further provided with a plurality of second wiring pieces, the second wiring pieces are in lap joint with taps on the low-voltage side of the transformer, and the double-station switching assembly comprises a movable contact set and a static contact set. The vacuum arc extinguishing assembly can disconnect the electric connection with the movable contact group and the static contact group under the linear driving of the first driving assembly and carry out vacuum arc extinguishing. According to the invention, transformer oil is not polluted in the capacity exchange process, the service life of the moving contact group is prolonged, the layout is compact, the size is small, and the switch cost and the transformer cost can be effectively reduced.