The prices of safety PLC and its ancillary equipment are much higher than that of ordinary PLC system.In order to solve this problem,a secondary development to the original control system is carried out.By using the technology of safety bridge,seamlessly integrated safety IO modules with legacy PLC system equipment,finally,the traditional PLC system has the safety control function of safety PLC.Based on a port automation project in Huanghua,this paper describes the practical application of safety bridge technology in this project.