The formation mechanism and influencing factors of cold island effect of air-source heat pumps （ASHP） were studied by means of fluid simulation and field test. Both the field test and simulation in a real unit in Changchun show that when there are surrounding buildings and ambient wind is 4.92 m/s, the cold exhaust air will affect the downstream air temperature and inlet air temperature of finned tube, making the inlet air temperature of finned tube decrease by 0.15-0.18 K. The heat transfer flux, fan flowrate, the outdoor unit accumulation, ambient wind and building shape are the main factors influencing the cold island effect of ASHP. The degree of cold island effect has a positive correlation with the heat transfer flux and a negative correlation with the fan flowrate. In the case of no ambient wind and buildings, the cold exhaust air diffuses along the ground to the environment. Under the condition of no ambient wind, when the heat transfer flux is 52.8 kW and the fan flowrate is 3.4 kg/s, the recirculation start time is 38 s, the final cold recirculation rate is 28%, and the temperature difference between ambient temperature and inlet air temperature of finned tube is 6.08 K.
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