Abstract: In order to realize automatic control of road dust suppression spray in the plant area of Zhangzhuang Concentrator of Masteel Mining，the improvement of control mode is studied，and the control mode，working principle and application on Siemens 1200PLC are introduced. The weather is monitored by adding rain and snow detection sensors，temperature and humidity sensors and other instruments，and the monitoring data is transmitted to the Siemens 1200PLC. Then，through the internal logic control of the PLC，the spraying is stopped in rainy and snowy days，and at night. When the temperature outdoor is freezing point，the spraying stopped，which realized spraying warning function. The successful application of the control mode has solved the problem of timeliness of manual operation，effectively saved water resources，and achieved high-quality dust reduction effect.

Key words: Siemens 1200PLC, rain and snow detection sensor, temperature and humidity sensor, DTL, analog quantity