A new depositional model in droughty climate, named flood-overlakes, is built in this paper. Rivers of the province act as seasonal flood under droughty, most of the rivers fade away in the hungriness, river water was drained out in the way of surface vaporation, vegetation ecology consumption, underground seepage, terminal river-lakes and river overflowed lakes, so that no whole catchement center nor the lacustrine sediment were formed. Thus, the basin filling characters are clearly different from that of the classic lacustrine depression basins and that of the shallow lacustrine basins. As a new type of depositional model in Mesozoic and Cenozoic, flood-overlake has important theoretical and practical sense.