Latent heat thermal energy storage technology is applied to air-source heat pump systems in cold regions to improve their adaptability. Heat is stored during the day and released at night. A simulation is conducted in this study to further investigate the heat storage and discharge characteristics of the system and the effect of applying multistage PCMs (phase-change materials). The results show that the heat storage capacity varies linearly with the charging time

where 18.94 kW?h is achieved at 380 min

and the average COP is 2.51. The heat discharge capacity first increases linearly and then reaches 13.58 kW?h at 180 min. When the inlet water temperature is 35 °C

the system stabilized after six continuous cycles

and its energy storage efficiency is 99.06%. The charging time of the three-stage PCM is reduced by 9.60%; its COP is increased by 3.97%; its total exergy efficiency is increased by 4.84% compared with those of a single-stage PCM. Reducing the melting point of the PCM in the subcooled zone is key to improving the system performance.