An xDSL (Digital Subscriber Line) modem (160) includes a setting module (168), a detection module (164), and a distinguishing module (166). The setting module pre-sets a threshold value, and adjusts the threshold value according to noise types. The detection-module captures connection parameters of the xDSL modem and the central office (CO) (120), and computes a judging value. The distinguish module distinguishes noise types according to the judging value, and determines whether the connection is maintained or disconnected. A method for stabilizing connection between an xDSL modem and a CO is also provided.