On-machine measurement and testing takes machine tool as hardware carrier to realize the integration of processing and measurement, which is of great significance to improve product quality and production efficiency. This paper introduces the composition and implementation process of the in-situ measurement and testing system for NC machining, and tests the performance of the system. The results show that the in-situ measurement and testing system for NC machining of large structural parts can realize the size and position errors in the process of large NC machining parts. Position measurement greatly shortens the positioning time of large NC parts, effectively improves the efficiency and qualified rate of one-time clamping, avoids the second clamping of workpieces, reduces the production cost, and provides a strong guarantee for digital assembly.