Abstract: The rough location of lake shoreline was confirmed for the Chang-8 oil Formation of the Yanchang Formation from Fengdikeng-Hongde area of Erdos basin, through the integrated study of geochemical patterns of Fe element in combination with lithology, grain size distribution, sedimentary structures, fossils and stratigraphic sequences. Integrated information from the region made it possible to precisely draw out the boundary between the braided river delta plain and delta front during the period the Chang-8 oil Formation was deposited. The boundary, in fact, is close to the shoreline of the lake. The results offered a reliable geological reference for palaeogeographic reconstruction and are very helpful for oil and gas exploration in the region.