In order to improve the reliability of power line communication , a improved model of G3-PLC physical layer specification based on LDPC encoding / decoding were proposed. In the improved model, the RS encoding / decoding function modules in the G3-PLC physical layer specification were replaced by the LDPC encoding / decoding function modules respectively. According to the G3-PLC physical layer specification, the LDPC encoding and decoding function were realized. The G3-PLC physical layer specification model and the improved physical layer specification model were built respectively in the Simulink software, the validity of the improved model were confirmed. The improved model provides a reference for the application of LDPC to the system design based on G3-PLC specification.