Aiming at the problems of measurement error,low efficiency and high cost caused by off-line measurement when measuring the dimensional accuracy of precision parts in CNC milling,the macro program for online detection and error compensation of parts was compiled by assigning relevant detection paths and compensation parameters,and the control system for online detection and error compensation macro program based on SKIP command of Mitsubishi M70 CNC System was developed.The application results show that the system can achieve the accuracy of 0.001 mm to 0.003 mm for online detection of repeated positioning,which can be applied to the CNC milling of precision parts,and has a certain value for promotion and use.