clipping is one of basic problems in computer graphics.Some condtions relating to clipping will be met when people draw grid contour

such as some sheet or ringy region without date point

region's boundary

some region with inaccurate interpolation point. However

at present

some famous clipping algorithms home and aboard are almost impossible to process grid contour's clipping after it is smoothed because time complexity is too high and region is too complicated.In this paper

an algorithm suit for the clipping of grid contour to solve the problem is presented. The algorithm may be summed up the following three steps:①filling the clipping region with -2.0 by calculating the point of intersection between contour and clipping region and sorting the point of intersection and partnering the point of intersection.②recording the direction of trace of contour from every boundary of clipping region.③increaseing the end condition of contour that begin from some boundary of clipping region and to own boundary or other clipping region' s boundary.As a result

the algorithm passed the test of practical large data.The examples shown in the paper and other applied examples demonstrated that the method of clipping is fast and effective for complex region of grid contour.