A centralized selflubricating system was introduced which was transformed from a handpressure lubrication for the ZTXX30A NC milling machine. A control circuit for this centralized selflubricating system was designed. Design ideas for the control ladder diagram and the alarm & protection were proposed and corresponding control ladder diagrams were written. The design principles of pump oil time ladder diagram, pump oil intervals ladder diagram and the alarm & protection ladder diagram of the lubricating pump were expounded. It provides technical supports for designs of centralized automatic lubrication systems for other CNC machine tools.