Information on the stoichiometry of carbon(C), nitrogen, (N) and phosphorus (P) in soils and its effects on community productivity and species richness in desertified grassland is essential to understanding the interactive relationship between soil and vegetation in the process of grassland desertification, and reveals the ecological mechanisms of land desertification. In this study, we measured organic C, total N, total P concentrations, and C:N, N:P, C:P in the topsoil of different desertified grasslands in the Horqin sandy land, and statistically analyzed the correlations among C, N, and P stoichiometry, community productivity, and species diversity. The results showed that the concentrations of organic C (1.39 mg/g), total N (0.117 mg/g), and total P (0.079 mg/g), and the C:N (7.50), N:P (2.22), and C:P (16.91) ratios in the topsoil of desertified grasslands remained at relatively low levels in contrast to the results nationwide or worldwide. It was not surprising that soil C, N, and P significantly decreased during grassland desertification. Their ratios, however, also significantly decreased in the gradient of desertification, suggesting an asynchronous loss of soil C, N, and P in the process of desertification. We found that topsoil organic C, total N, total P, and their ratios were positively correlated, suggesting a coupling relationship among organic C, total N, and total P in topsoil in the study sites. Further, the coupling relationships between organic C and total P did not change with the development of grassland desertification. Expectedly, community productivity was limited by the loss of soil nutrients in desertified grassland in this study. However, soil N:P stoichiometry could explain more variations of community productivity than soil N or P concentration could. Similarly, correlation analysis showed that species richness was significantly correlated with soil N, but not P. The diversity index was significantly correlated with soil N and P. Compared with N or P concentration, the soil N:P stoichiometry effectively reflected the influence of nutrient balance on species diversity.