The present application provides an air-cooling heat pump system and a refrigerant leak detecting method and system therefore. The 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. According to the refrigerant leak detecting method of the present application, it is possible to accurately and reliably determine whether or not the refrigerant of the system to be detected leaks and the leak degree.