When wireless communication technology is applied between Front-end Equipment and Background on expressway, the security is always an important point to be considered. The paper put forward a kind of reliable communication with the PSAM Technology and private communication protocol. The PSAM technology is used to encrypt the plain text. The private communication is formulated to achieve a high reliability of communication mode based on 4G transmission equipment. In the end, the experiment was conducted to demonstrate its feasibility and really high security. Keywords—expressway communication; pivate protocol; session layer; PSAM