Abstract: According to the result of Moving-t test analysis, The changes of rice-seeded area during the past 50 years are divided into three stages, 1949-1968, 1969-1985 and 1986-1996, in Beijing, and two stages, 1949-1971 and 1972-1995, in Tianjin, respectively. In both regions, the rice-seeded areas show the fluctuation from rise first and then fall down. And before 1970, the changes in the two regions were, on the whole, similar. But after 1970, the changes in the two regions tended to difference. The changes of rice-seeded area in both regions were all resulted from the comprehensive influence of the natural, the technological and the political factors. It is the faultiness of the policies that has made the rice-seeded area being extended over the capability of water resource supply. In order to serve the need of the rice planting, the exploitations of water resources in both regions all have been extended from rain to surface water and then to groundwater. But when the water resources still could not meet the need, the rice-seeded area was reduced. As a response of farmers to the annual rain variation, the variation of rice-seeded area is lagged behind that of the rain by one year, which resulted in the remarkable negative correlation features between the precipitation of a year and the rice-seeded area of the same year. Such important phenomena makes the water resources can not be used sufficiently in the years with more precipitation, but the shortage of water resources be strengthened in the drought years.