Abstract: This paper presents a testing principle for intersect of sight line and a new method of eliminating hidden lines for complex object. The distinguishing feature of the new method is that a complex object can be decomposed to several convex parts of the body,Then,the periphery of projection for the convex part of the body is found.At the same time,the intersects of the line to be eliminated and the periphery of projection for the convex part of the body is sought.The line to be eliminated is divided by the intersects. The sight of the lines is tested. Last,the projection of eliminating hidden lines for complex object is obtianed.