A method for detecting radio frequency interference (RFI) is provided. The method includes the following steps. Parameters of at least two pairs of digital subscriber lines (DSLs) are acquired. Sub-carriers having RFI in each pair of the at least two pairs of DSLs are detected according to the parameters. The number of line pairs having RFI on the same sub-carrier in the DSLs is counted, and if the number of the line pairs occurring RFI on the sub-carrier is greater than a preset threshold, or if a ratio of the number of the line pairs occurring RFI on the sub-carrier to a line pair number of the at least two pairs of DSLs is greater than a preset threshold, it is determined that RFI exists at a frequency corresponding to the sub-carrier. A device and a system for detecting RFI are further provided. Therefore, RFI frequency existing in xDSL can be detected.