The invention relates to a defrosting system and method for an air source heat pump. According to the technical scheme, the defrosting system comprises an anti-freezing water tank, a defrosting tube 1, a defrosting tube 2 and a water pan, wherein an electrical heater is arranged in the anti-freezing water tank; the water pan is arranged at the lower part of an evaporator; the defrosting tube 1 and the defrosting tube 2 are mounted on the evaporator; an anti-freezing solution in the anti-freezing water tank is connected to the defrosting tube 1 in the evaporator through an anti-freezing water pump and a pipeline and connected to the water pan through the defrosting tube 2; an ice melting tube is arranged in the water pan, and an outlet of the ice melting tube is connected with the anti-freezing water tank, so that circulation of the anti-freezing solution is realized. The defrosting system and method have the benefits as follows: the water pan is separated from a supporting plate of the evaporator and fixed below the evaporator at a certain interval, the situation that defrosted water freezes in the water pan and accumulated upwards along the bottom of the evaporator is avoided, the ice melting tube is arranged in the water pan, and accordingly, condensate water can be prevented from freezing in the water pan.