By using species richness,Shannon-Wiener index,Simpson dominant index and Pielou evenness index,Species diversity study was made in the lands which converted from farmlands to forest or grassland for 3,4 and 5 years in Northwestern Shanxi Province.Research results showed that the species richness and biodiversity index was increased gradually,and the dominant index of them decreased with the elongation of rehabilitation in these converted land.Species diversity of these lands evidently increased.