Abstract: The Bitahai wetland is one of the most important wintering sites of the Black-necked Crane (Grus nigricollis) because of little human disturbance and good habitat. Food is the determinant factor that influences the long term survival of Black-necked Cranes. To understand the ecological requirements of this bird and then make matching conservation measures, it is important to figure out their feeding habits and the food nutritional components. We used the standard quadrat method to employ underground food composition and biomass. Then we analyzed the nutritional components of each food using the standard method. We found 10 plant species with rhizome or tubers that could be the food of Black-necked Cranes and the total biomass was 926.30 g/m². Sanguisorba filiformis and Blysmus sinocompressus were the key food plants and accounted for 47.75% and 19.96% of the total biomass, respectively. Sanguisorba filiformis included more crude protein and crude fat, and less crude fiber, therefore the Black-necked Crane may prefer the Sanguisorba filiformis rather than Blysmus sinocompressus. We provided the basic information of underground food items and food nutritional components on Black-necked Cranes at the Bitahai wetland, and the information has been useful for the conservation of endangered Black-necked Cranes.