the text is a introduction of the formation and operating theory of a pumped frequency-changed controlling system on the base of PLC,the system adopts the frequency-changing and speed－adjusting form to adjust the rotate speed of the water-pumped mechine automaticly,keep the water pressure at a certain level,the system can use PLC to programme the controller,the frequency-changer,the PIDinstrument,pressure changing and delivering body to fulfill the task of controlling logic,changing frequency and adjusting speed,self-checking of instrument,warning of the trouble,etc. To realize the self-controlling,starting the pump automaticly when the fire begins.未完待续