Siemens S7-200 PLC was suitable for small control system with DI/DO channel, which was extremely convenient for digital signal control. However, its processing effect of analog signal was relatively poor. This equipment had high requirements for site environment, and it not only had poor signal anti-interference ability, but also needed to add?EM231 / 235 module and the hardware cost was also high. As a result, the method of collecting analog data by means of communication was proposed. At the same time, 16 road inspection instrument and S7-200PLC communication technology were introduced. Therefore, the patrol instrument adopted standard Modbus protocol, the transmission mode was RTU mode, patrol instrument and S7-200 transmitted data through MODBUS communication, which saved hardware cost, reduced strength of compress and maintenance difficulty. The communication between patrol instrument and S7-200 was realized by Micro / WIN MBUS instruction, as well as built OPC channels in WINCC through KEPServer V4.0 software, which implement upper and lower communication. The results showed that this method had advantages of simple connection, reliable transmission and low hardware investment.