According to similar natural condition and different years of de-farming, this research studied nitrogen variation features of the desertification soils of different de-farming and wasteland in the western Karst region, Guizhou province. The result shows that the content of soil organic matter,total nitrogen and different forms nitrogen decreased firstly, then increased by time pasted. Based on this conclusion, and effect of heat and water in this region, the paper deduced that it is possible to restore the nitrogen fertility under natural condition.