The Erlian basin is consisted of a group of middle Mesozoic and Cenozoic small fault lake basins, and it is geologically favorable for the formation of stratigraphic-lithologic reservoirs. Considering that these fault lake basins are characterized by small size, multiple sources, rapid deposition and abrupt facies belt change, this paper focuses on the formation process of sedimentary sandbodies distribution and analyzes the key factors controlling of sandbodies in terms of source material supply, transport pathway and sandbody distribution by means of research techniques of palaeostructure analysis, seismic sedimentary facies analysis and typical sedimentary sandbody analysis. It is indicated that the key factors controlling sandbodies distribution are the ancient material source, ancient valleys and slope breaks. Entry position and distribution of depositional systems are controlled by the sag margin and the internal ancient highlands. The transport pathways of sandbodies within the lake basins are controlled by ancient valleys formed by sag-controlling faults. In different types of slope break zones, the sandbodies present different characteristics of superposition and distribution. The an?cient material source, ancient valleys and slope breaks in fault sags are influenced mutually and have a significant effect on the forma? tion and distribution of sandbodies jointly.