At present, the first round revisions of the county towns’ overall plan have been nearly completed in our country. Among them, there are many experimental samples which are reasonably planned and constructed, however, the phenomena that the standard of the plan is too high and the scale is too large. This paper tried to probe into the question how to determine the reasonable scale of the population in county towns tentatively, at the beginning of the paper, the author analyzed the elements that affect the scale of the county towns’ population.