A method for identifying an electronic apparatus is provided. The method is adapted for a monitor apparatus in a power system, and includes the following steps of adaptively updating a power signature database related to at least one electronic apparatus; adaptively updating a line resistance database related to the monitor apparatus; detecting whether at least one power signature event occurs; calculating a system impedance of the at least one power signature event when the at least one power signature event occurs; and identifying at least one unknown electronic apparatus resulting the at least one power signature event according to the system impedance, the power signature database and the line resistance database.