The invention discloses an ultra-low ambient temperature solar-air source heat pump unit connected with a sustainable heat source. device, main circuit electronic expansion valve, outdoor heat exchanger, gas-liquid separator, auxiliary circuit electronic expansion valve, water-cooled evaporator, low-temperature solar collector, water pump, first one-way valve, capillary tube, second one-way valve, second 1st solenoid valve, 2nd solenoid valve, 3rd solenoid valve, 4th solenoid valve, 5th solenoid valve, 6th solenoid valve, 7th solenoid valve, main loop (heating / cooling operation), defrosting loop, Supplementary air loop and sustainable heat source loop. On the one hand, the unit can use the hot water produced by the solar collector to heat the refrigerant in the air supply loop to vaporize it under the air supply working condition. On the other hand, in the defrosting condition, the four-way reversing valve of the unit does not change direction, and the hot water produced by solar energy is used for defrosting when the indoor heating is continued.