The programmable logic controller(PLC) has advantages of high reliability , easy operation and good on-site adaptability etc,thus it was praised as one of automation mainstays of processing industry.According to the operating situation of hexahedral head hydro-machine used currently for manufacturing of artificial diamond in China, including the requirements of manufacturing technology,the authors describe the reformation of the controlling circuit by use of PLC, make a brief introduction to the composition and protection of PLC controlling system, and say a few words about their experience in operation of PLC.