The present application provides a data processing method, a refrigerant leak detecting method, a system performance detecting method and a system fault detecting method. The steady-state data processing method includes: (i), resetting a cumulative change of target determination data and a data detection period as 0; (ii), obtaining the detected target data; (iii), calculating the cumulative change of the target data; (iv), when the calculated cumulative change of the target data is less than its preset threshold, adjusting the data detection period and returning to (ii); or recording a data detection period when a cumulative change of any of the target data is not less than its preset threshold; (v), when the recorded data detection period is less than its preset time threshold, determining a target data result obtained in the period as unsteady-state data of the device; or when the recorded data detection period is not less than the preset time threshold, determining the target data obtained in the data detection period as steady-state data. According to the method, the steady-state data can be obtained and subsequent analysis and processing can be performed.