A device and a method for detecting a refrigerant leakage of an air source cooling-only system, wherein the detection method comprises S1: obtaining an operating parameter of an air-cooled cooling-only air source cooling-only system, wherein the operating parameter comprises at least a compressor speed or capacity; S2: comparing the operating parameter with a preset operating parameter interval; S3: updating a cumulative score when the operating parameter falls within the preset operating parameter interval; and S4: determining that a refrigerant leakage has occurred when the cumulative score exceeds a predefined cumulative score, and returning to step S1 when the cumulative score does not exceed the predefined cumulative score.