County towns are not only the center of economy, politics and culture but also the "main force" in rural area. County is a very steady administration unit in its long history. A county is a cultural regional unit and county town is its center. Among different counties there is much difference, but there is much sameness inside a county in historical culture. So the county towns bring into play very important functions in rural area. County towns both are the "cities" in rural area and the "rural" in cities. So county towns bring into play bridges and ligament functions in cities rural reciprocity. This article based its viewpoint on modern conditions of China and put forward that those 1780 county towns are keys in course of small towns constructing. So we must emphasize the construction of county towns at first.