Function in analysis of spatial point pattern is one of the prevalent analysis tools for studying population spatial pattern，and the method of edge correction is the key part of the function. The method of area ratio，the area of a circle in sample plot to the whole area of the circle, in which the distributing point is the center and the scale distance is the radius，is defined as the weighted coefficient of edge correction in this paper. Spatial distribution pattern in the population of Chilo supperssalis was analyzed using the method of area ratio. Results indicate that the function can reflect the spatial distribution pattern of insect population in different scales, and are of benefit to make a reasonable plan in sampling. It also shows that the sampling-size in chilo supperssalis should be not less than 2m in field.