The problem of establish the parametric library of bolt connecting piece in ACAD was analyzed, and a method of the design of parametric library of bolt connecting piece based on ACAD graph block was put forward. This method decomposed bolt connecting piece assembly drawing into basic graphic block, fit the basic graph block into the bolt connecting piece assembly drawing with the assembly relation. Comparing with the usual method, this method had the advantages of simple manufacture, avoiding writing the complicated parametric drawing program, drawing speed etc.

This paper analyzes the problem of lines duplication, overlap and discontinuity in the application of AutoCAD. And it also proposes a method of automatic elimination of duplication, overlap and discontinuity by using the VisualLISP language embedded in AutoCAD system. After the processing, the engineering drawings can avoid linear problems which do not conformity to the requirements of the national standard, and can also avoid the complex work of manually modifying on the complicated lines. The processing of repetition elimination in sheet cutting diagram is possible to extend the life of the laser cutting head and the cutting accuracy of the spare part. After the computer graphics repeating the eliminate processing, it can effectively improve the recognition rate of computer graphics automatic scoring system.