Because of human beings activity,the world's natural ecosystems have been partly destroyed and suffering serious desertification.It's now an urgent problem to harness desert for human being's living.In this paper,the author studied the reasons affecting land desertification and tries to extract the determinant ones by principal component analysis.The actuality of every county in Inner Mongolia are different,the reasons causing desertification are different too.But population increasing,farmland spreading,natural resource being used inconsequently are main reasons of desertification.By comprehensive analyzing of many factors,the author points out the main countermeasures to manage the desertification land.