The Siberian Crane (Grus leucogeranus), an IUCN Critically Endangered species, comprises 3 500﹣4 000 individuals, with about 98% of its global population wintering in the Poyang Lake, China. Originally, Siberian cranes fed tubers of submerged plants, especially the Eel Grasses (Vallisneria spp.) in shallow water habitat of the lake. However, in the past few years, as the agricultural fields became their important foraging places, the diet of the Siberian Crane should have changed. To study the food composition of Siberian cranes in agricultural fields, we used microscopy method to analyze 70 fecal samples collected from 5 rice paddies and 2 lotus ponds during November 2017 and April 2018. We also collected plants at the foraging grounds to construct a referencing library of plant cell morphology, which was used to identify plants in fecal samples. Frequency conversion method was used to calculate density of each food resource. The food of Siberian cranes composed of 15 plant species belonging to 10 families (Table 1), with Rice (Oryza sativa, relative density 34.34%), Lotus Roots (Nelumbo nucifera, 22.99%), and Chinese Milk Vetch (Astragalus sinicus, 10.61%) being their main food items. However, the tuber of eel grasses, which formerly was their typical food, became extremely low proportion (2.05%). Therefore, the diet of Siberian cranes has changed very much, with the crops becoming their important food, as the degradation of submerged plants in the Poyang Lake. Foraging in agricultural fields, the Siberian cranes are facing a series of problems, especially high intensity of human disturbance. To provide a safe and stable foraging environment for cranes, we propose some protective measures, including enhancing environment education, promoting ecological compensation, restoring submerged plants, and constructing mini protected areas.