Water real-time management and automatic control is very important to water-saving technique in Xinjiang. In condition of production practice, a decision support system for drip irrigation under plastic film on cotton (CDIDSS) is developed by key technique of DBMS and MBMS and KBMS and WBMS. Sorts of sensors to put on cotton field acquire real-time data. Through decision command by calculation and analysis of acquired information, control system may perform automatic control of irrigation facilities. So irrigation period of effectiveness has improved by CDIDSS.