Abstract: In order to give an overview on nutritive value of some common forage grasses in desert steppe area of Maowusu Sandy Land, the samples of the forage grasses mainly observed in this region were collected in the four seasons, respectively, and their normal nutritional components were determined and statistically analyzed. In summer, there were complete varieties of forage grasses, higher grass yield, longer grazing duration, and higher grass nutritive value. Accordingly, the carbohydrates and proteins of the grass samples collected in summer were subjected to classification analysis by using Cornell net carbohydrate and protein system（CNCPS）. Furthermore, the existence of difference between the content of biodegradable protein（SCP） determined by CNCPS analysis method and the content of protein content（CP） evaluated by feed proximate analysis protocol was identified. The results showed that the dry matter rate of the main forage grasses in desert steppe area of Maowusu Sandy Land was observed to follow an elevating trend from spring to winter（P 〈0.05）; the protein content of the grasses varied greatly between the four seasons, except for Potentilla chinensis, it showed a gradually decreasing tendency in the other tested forage grasses from spring to winter; the neutral detergent fiber（NDF） and acid detergent fiber（ADF） were generally increased from spring to winter and expressed seasonal variations. The difference in SCP and CP were found in the samples of Achnatherum splendens, Leymus chinensis, Potentilla chinensis, Carex duriuscula, and Flos inulae collected in summer. The combined data suggest that the nutritional characterization of forage grasses using CNCPS is more accurate and detailed. Our results provide basic theoretical data for the scientific utilization of grassland.