A method for testing a subscriber line of a PABX (Private Automatic Branch eXchange) using a DTMF (Dual-Tone Multi-Frequency) signal. The method includes the step of controlling a DTMF transmitter in response to a line test request from an exchange operator to transmit the DTMF signal to the subscriber line, the step of receiving a component of the transmitted DTMF signal reflected from the subscriber line due to impedance mismatching, and the step of determining from a strength of the received DTMF signal component whether the subscriber line is abnormal.