Abstract: Taking two-leg shield hydraulic support as example, design of an automatic control system of hydraulic support based on S7-300 PLC was introduced. The system makes intelligent analysis with software of control system for data measured by sensors of pressure, shrinkage and angle which are installed on column, so as to realize start-stop of magnetic valves, which can make autonomous operation of hydraulic support. The actual application showed that the system realizes on-line monitoring and control real-timely for hydraulic support of coal mine underground.