In the NC milling programming,programmers often realize the programming of removing the allowance of part through increasing offset value and calling subroutine.This approach is feasible if curvature radius of contour is large,but when there is a smaller curvature radius in outline,system will produce interfere alarm that tool radius are too big and terminate the program running.In order to solve this problem,convenient programming example by calling subroutine was given.The interference situation occured in the process of tool compensating was analyzed,the method of forecasting and mathematical treatment for interference of tool compensation was proposed,the ideas and processes setting up the anticipation mechanism of tool compensation interference by macro program were given and the programming examples were present.This method is effective to solve the engineering technical problems in programming.