The invention discloses an air source low-temperature 
heat pump water heater, comprising a main 
machine, a thermal storage heat insulating water tank, a controller, a four-way valve, a jet 
enthalpy increasing compressor, a high-
pressure switch, a sleeve condenser, a reservoir, a 
drying filter, an 
electromagnetic valve, an assistant 
thermal expansion valve, an 
economizer, a main expansion valve, afin 
evaporator, a gas-liquid separator, a low-
pressure switch and a 
check valve. The D direction of the four-way valve is connected with a gas discharging 
pipe of the jet 
enthalpy increasing compressor through the high-
pressure switch, the C direction is connected with a gas inlet of the sleeve condenser, the S direction is connected with a gas absorbing port of the jet 
enthalpy increasing compressor through the gas-liquid separator and the low-pressure switch, the E direction is connected with a gas outlet of the fin 
evaporator, an outlet of the sleeve condenser is divided into two paths after passing through the reservoir and the 
drying filter, the main path directly enters the 
economizer and then enters a liquid inlet of the fin 
evaporator through a main 
thermal expansion valve, the secondary path enters the 
economizer through a liquid path 
electromagnetic valve and the assistant 
thermal expansion valve, and then enters an assistant gas inlet of the jet enthalpy increasing compressor through the 
check valve. The invention can ensure the supply of hot water all day in every season in northern places.