Abstract: In the process of large and medium-sized precision workpiece machining on the automatic production line, there are difficulties in position handling, high machining accuracy requirements, difficulties in repairing machining defects, and large losses and other problems. Using Renishaw's OMP60 probe and tool setting instrument, combined with FANUC FOCAS software library, real-time acquisition and monitoring software of machine tool is compiled by C#, and a set of on-line position alignment, dimension measurement and tool monitoring system is constructed with NC system G program and macro instruction. It realizes automatic positioning of workpiece and online monitoring of tool breakage, guarantees the machining quality of workpiece and meets the continuous production demand of large precision workpiece on automatic line.