[Objective] To investigate the influence of enclosure ages on community structure and species diversity of sandy grassland in Yanchi County of Ningxia Hui Autonomous Region, for revealing the change rule of vegetation restoration in the enclosed sandy grassland. [Methods] Taking the non-enclosure and enclosed sandy grasslands in 5, 10, 20 years as research objects, the influence of different enclosure ages on the community structure and species diversity in semi-arid region was carried out by using the method ofspace-for-time subotitution. [Results] The dominant species in not enclosed areas were annual and biennial herbs. In enclosed areas, they were shrubs enclosed for 5 years, perennial herbs and shrubs for 10 years, perennial herbs for 20 years, respectively. Comparied with not enclosed area, the index values of vegetation cover, community density and biomass were increased obviously in 5 and 10 year enclosed areas, while decreased a little in 20 year enclosed area. [Conclusion] The long-term enclosure could not improve the productivity of sandy grassland vegetation. The enclosure ages less than 5 years can promote vegetation restoration, but it plays an inhibitory role when the enclosure ages was more than 10 years. In the short term, enclosing measures promote vegetation restoration, but for long term, enclosure plays an inhibitory role.