For land-to-air missile weapon system simulation, most problems can be abstracted as the problems on the relationship between the target and the given region (polygon). In this paper, the conceptions of Rotary Function and correlative edges are proposed. By integrating rotary function with correlative edges, a new algorithm of point in-out polygon is put forward. The new algorithm transforms the relationship between a point and a polygon into that between a point and its correlative edges. This paper firstly finds the correlative edges of the point, then, calculates the value of the rotary function of the polygon that assembled by the point and its correlative edges, finally, by analyzing the value of the rotary function, the relationship between point and polygon can be sure. Because lots of operations of intersection are avoided, the efficiency of the algorithm is raised radically. The use of the new algorithm can effectively and simply solve the critical position problems in the traditional algorithm. Software implementation verifies the high robustness and efficiency of the new algorithm. The model constructed in the paper is strong in reuse for multi-type land-to-air missile weapon system simulation, and the study in this paper is important to avoid overlapped study and development.