With the development of modern science and technology, the development of electrical automation engineering has also become widespread. In the traditional sense, the wiring of the electrical automation control system is complex, the cost is high, the maintenance is difficult and failures may easily occur, and these factors seriously affect the system efficiency. The application of PLC technology in the field of electrical automation greatly simplifies the installation and operation process, and improves the work efficiency. Therefore, PLC technology has come to play an increasingly important role in the efficient and stable operation of electrical automation engineering. This paper analyses and explores the principle and practical application of PLC in the field of electrical automation engineering, and optimises the automatic control system based on PLC.