The relationships between sheep dung quantity and the organic carbon and total nitrogen contents within 5 cm of surface soil were studied by setting up sequential plots of six grades(1.41-1581.68 g/m²)according to sheep dung quantity grade formed naturally in Ningxia Hui Autonomous Region deserted steppe ecosystem.Models were then established for logarithmic sheep dung quantity,as an independent variable,and the surface soil organic carbon and total nitrogen contents,as dependent variables.Results showed the surface soil organic carbon content did not change significantly at a low level of sheep dung quantity,but changed obviously at a high level.The surface soil total nitrogen content changed obviously at a low level of sheep dung quantity.Ratio of soil carbon to soil nitrogen increased firstly and then decreased with the increased sheep dung quantity.Preliminary research concluded that sheep dung nutrients return is a very important process affecting soil organic carbon and total nitrogen contents under free grazing conditions in the deserted steppe ecosystem.The effect of the returned sheep dung quantity on soil total nitrogen began to appear when accumulated sheep dung quantity was at a low lever,but the net returns of soil organic carbon and soil total nitrogen contents were significantly enhanced at a higher level.The ratio of soil carbon to nitrogen showed a complex trend because of the interactive effect of the returned soil organic carbon and total nitrogen.