The invention discloses a data security transmission system. The system includes a communication server, a security terminal, a security service end and a communication terminal, and is characterizedin that the security terminal is located at a data exit of the communication terminal, a dedicated joint is used for solidification connection between the security terminal and the communication terminal, the communication server is connected through a network interface, the security service end is located at an information system data exit, and is connected with an information system through routers or a switches, and the security server realizes bypass accessing at a location between the communication server and the security terminal. According to the data security transmission system, all security functions are realized through the security terminal and the security service end, security functions of signature verification of information, message forwarding, certificate initialization and the like are realized, and the advantages that undeniability and integrity of transmission information are guaranteed, unauthorized tampering is prevented, a centralized management function for security terminal equipment can be realized, and service communication and management information reporting can be carried out through a service port are achieved.