The invention discloses a cascade heat pump air-conditioning unit comprising a surface cooling type heat exchanger whose shell side inlet and outlet are sequentially in serial connection and the first level and second level cryogen-air heat exchanger. The shell side outlet of a second level cryogen-air heat exchanger is connected with the fan inlet. A compressor, a cryogen-water heat exchanger and a capillary pipe are connected between the outlet and the inlet of the tube side of the first level and second level cryogen-air heat exchanger. One end of a water supply pipe connected with the water source and installed with a first stop valve is communicated with the tube side inlet of the surface cooling type heat exchanger and the water supply pipe is communicated with a water supply branch tube provided with a second stop valve. The other end of the water supply branch tube is connected with the tube side inlet of the cryogen-water heat exchanger. The tube side outlet of the surface cooling type heat exchanger is communicated with the water supply branch tube through a water supply return pipe. The tube side outlet of the cryogen-water heat exchanger is communicated with a water output pipe. The invention can perform cascade refrigeration and heating circulation and balance underground temperature field.