The invention relates to a physical layer communication method and device for a power line communication system. The method comprises the following steps: disturbing eavesdroppers by adding artificial noises, calculating an optimal solution of a receiver decoding matrix according to a mean square error to obtain an optimal solution of a transmit precoding matrix and an optimal solution of an artificial noise coding matrix, and finally separately coding useful signals and the artificial noises according to the two optimal solutions to construct an optimal transmit signal. Thereby, the artificial noises cannot disturb legitimate users, the threats of the eavesdroppers to power line communications can be suppressed on the basis of effectively guaranteeing the communications of the legitimate users, and the communication security can be improved.