Creating polygon is a normal arithmetic through turn left or right algorithm. According to the rule

polygons can be created by clockwise or anti-clockwise. But it may make some repeated and invalid polygons. The purpose of this paper is to introduce a method to judge polygon search direction and creat every polygon by only left algorithm. The method presented in this paper is to judge the polygons search direction to according to the angle changing between adjacent lines. Experimental results show that it is an efficient method to create polygons automatically and avoid invalid polygons.