By extracting the data of the number and spatial distribution of settlement sites in northern Shaanxi since Tang Dynasty,and combining the climate fluctuation in historic periods,we studied the controlling factors that affected the changes of the number and space of settlement sites in study area in last 1500 years. The number of settlement sites decreased temporally and decreased spatially from northwest to southeast gradually. By reconstructing the temporal - spatial distribution of settlement sites,we found that its controlling factors were closely related to the policies instead of desertification and climate change. Within the study period,the government implemented Jimufuzhou system to Dangxiang Nationality in Tang Dynasty. During the confrontation of Song and Xixia Dynasties,the Dangxiang people attached importance to develop agriculture,so did Song Dynasty. In Yuan,Ming and Qing dynasties,the number of settlement sites decreased,the government adopted the prohibition policy in the study area. The national policy was the main controlling factor for the change of settlement sites in study area.