A refrigerant leak detecting method for an air-cooling heat pump system in a heating mode comprises S110, S210, obtaining a leak indication parameter set, wherein the leak indication parameter set at least includes a refrigerant level in a liquid reservoir and/or a supercooling degree; S120, S220, comparing each leak indication parameter in the leak indication parameter set with a corresponding preset indication parameter interval; S130, S230, when each leak indication parameter falls within a corresponding preset indication parameter interval, obtaining and recording a corresponding evaluated refrigerant leak amount; S140, S240, when a cumulative value of the evaluated refrigerant leak amount falls within a preset refrigerant leak interval, determining that a refrigerant leak occurs in the air-cooling heat pump system; when the cumulative value of the evaluated refrigerant leak amount does not fall within the preset refrigerant leak interval, returning to the step S110, S210.