In this paper, the annual drought index during 1470-1979 in North China are calculated.It is shown that this region suffered from the most serious droughts which lasted the longest periods in the last 500 years. The annual precipitation and the precipitaion of May-September in this period were decreased at least by 10-50 percent than the normal precipitation in the same period. And it is shown that the frequent and serious natural colamity are the main factors affecting the stabilities of not only the social economy, but also the social politics.