A power line communication device and a power control method thereof are provided. The power line communication device, coupled to a power line in a power line communication system, includes a transmitter, a power coupler, a signal detector and a controller. The transmitter is configured to produce a transmit signal. The power coupler, coupled to the transmitter, is configured to couple the transmit signal to the power line. The signal detector, coupled between the transmitter and the power coupler, is configured to detect the transmit signal. The controller, coupled to the transmitter and the signal detector, is configured to adapt a dynamic range of the transmitter based on the detected transmit signal without conducting a channel sounding procedure.