It was explored that the drying trend of eastern China were divided by abrupt changes (280’s,880’s and 1230-1260’s).The changes of population during the last 2000 years were delineated and the percentage of people living in the northern part was calculated (table 1).It shows that during the early time,the population in the northern part got the higher percentage than that living inthe southern part.Then the percentage dropped rapidly at the 13th century, and had not recovereduntil now.Table 2 gives the percentage of population of provinces showing the population constractbetween the west and the east.It shows that before the 13th century the Shanxi/Shaanxi (westernpart) were almost the same with the Jiangsu/Zhejiang (eastern part),but afterward the easternpart got higher percentage than the western part.Cultivated land and tax were adopted here toshow changes of economy.Table 3 shows the percentage cultivated land and tax of the northernpart.Same conclusion are given as that shown in Tables 2 and 3.It hints that after the 13th century,a new geographical structure was set up.The relationship between the changes of demography (and culture) with the climate are tried toinvestigated in this paper.It has been discovered that the central government often lost their rulingover this country during the cold epoch.