The introduction of the system of thermal energy storage (TES) based reverse cycle defrosting method using sub-cooling energy of refrigerant for air Source heat pump(ASHP) is given firstly. And then the characteristic of TES using sub-cooling energy of refrigerant in heating is experimentally researched. The results show that storing sub-cooling energy of refrigerant in the PCM can not only improve the system COP in heating, but also provide energy for defrosting. Two modes of TES are inferred and it proves that improved system performances and indoor thermal comfort can be resulted in mode of starting TES process when heating for one hour.