The invention relates to a defrosting air source heat pump system. The defrosting air source heat pump system comprises a compressor, a reversing valve, a first solenoid valve, a first heat exchanger,a second solenoid valve, a first throttle mechanism, a second throttle mechanism and a second heat exchanger which are sequentially arranged on a refrigerating fluid loop; and a third heat exchangeris arranged on the second heat exchanger located outdoors in parallel. According to the defrosting air source heat pump system, on one aspect, the system successfully solves the problem about the low-position heat sources (low-grade heat energy which cannot be directly used and includes air, soil, water, solar energy, industrial waste heat and the like) during defrosting, and the problems that thedefrosting time is long and the defrosting reliability is poor due to the fact that no low-position heat sources exists during frosting are solved; and on the other aspect, the system takes heat fromthe outdoor environment, the problem that during traditional defrosting, the low temperature refrigerating fluid flows through the indoor heat exchanger, and therefore the poor thermal comfort causedby indoor environment temperature fluctuation when heat supply is recovered is solved.