Grassland has sustained serious desertification due to inappropriate human activity in arid and semi-arid areas. This desertification has disrupted ecosystem structure and function. However, desertification on the grassland's C:N:P stoichiometry (Carbon, Nitrogen, and Phosphorus) are poorly understood, which undermines management and restoration of desertified grassland. To improve our knowledge, we studied a desertification gradient in Northeastern China's Horqin Sandy Land to determine the effects of desertification on ecosystem function, the plant community, and soil C:N:P stoichiometry. The soil and plant community C, N and P pools decreased during desertification. Under severe desertification, the soil C:N decreased by 17.4%, versus 39.2% for C:P and 50.1% for N:P. This implies non-proportional losses of soil organic C and nutrients, with the greatest loss for organic C, followed by total N and total P. Plant aboveground C:N and C:Pand belowground C:N increased, suggesting increased nutrient utilization efficiency. Canonical correspondence analysis ordination showed that soil N and P significantly affected the plant species composition, which was associated with plant C:N:P. The desertified grassland's fertility (especially N) directly determined the plant community C, N, and P concentrations and C:N:P ratios. The increased dominance of two psammophytes, Agriophyllum squarrosum and Artemisia halodendron decreased plant community C, N, and P concentrations, but increased C:N and C:P. Thus, plant community C:N:P stoichiometry was mediated by soil nutrients and plant functional groups driven by soil nutrient changes during desertification. The soil nutrient imbalance potentially changed plant community composition, this then altered the soil chemical composition because plant species differ in their element contents and litter inputs. Hence, species with high N content could improve grassland restoration by mitigating N limitations. The native psammophytes A. squarrosum and A. halodendron, with high stress resistance and resource utilization efficiency, could be applied in desertified grassland restoration.