We studied the diversity, timing characteristics and frequency of flower-visiting insects on a degraded typical grassland with three enclosure durations in Xilinguole, Inner Mongolia. Experimental treatments included plot A (enclosed in 1983), plot B (enclosed in 1996) and plot C (free grazing). A total of 2131 individuals, 183 species belonging to 7 orders and 71 families were collected from the 3 plots. 1133 individuals of 154 species belonging to 7 orders and 60 families were from plot A, 847 individuals of 158 species belonging to 6 orders and 158 families were from plot B, and 151 individuals of 21 species belonging to 3 orders and 13 families were from plot C. Plot A had the greatest individual number of the flower-visiting insects, plot B had the highest richness, while plot C had both the lowest individual number and richness. The Shannon diversity index (3.12), Pielou evenness index (0.86) and Margalef richness index (7.16) were the highest in the plot B in July. The BergerParker dominance index (0.15) was the highest in plot C in June. The change trend of Shannon diversity index in different months was consistent with that of Pielou evenness index, but contrary to that of BergerParker dominance index. The Jaccard community similarity was the highest between the plot A and plot B (0.25) and the lowest between the plot A and plot C (0.16). The dominant flowervisiting insect species varied with plots and months and in flower-visiting frequency.