Abstract: Researches on fine-grained deltas mostly focus on the sequence evolution of their deep-water environment. However, the short-term development process, geometric form, deposition mode and sand body distribution of fine-grained river-dominated delta in the gentle slope of lakes are still unclear. Using sedimentary forward numerical simulation, this paper rebuilds the growth and evolution process of fine-grained river-dominated delta in the gentle slope of lakes, contrasts and analyzes the morphological characteristics of silt-rich and shale-rich deltas, and establishes a depositional evolution model. In combination with the satellite imagery and field surveys of Gongba river delta in the Daihai lake, the paper studies the similarities and differences between the actual sedimentary system and the sedimentary forward numerical simulation results, and summarizes the distribution law of sand body. The research results show that:(1) The sedimentary evolution of the river-dominated fine-grained delta in the gentle slope of lakes can be divided into two modes:normal lacustrine regression and forced lacustrine regression. During normal lacustrine regression, under the control of the crevasse and bifurcation of the main distributary channel, the superimposed bodies of the multi-stage distributary channel and the mouth bar (channel-mouth bar complexes) underwent a dynamic process of accretion, abandonment and transformation, and finally were unevenly distributed on both sides of the main distributary channel. During forced lacustrine regression, the distributary channel-mouth bar complexes of the multi-stage strandline are connected by the main distributary channel in a delta plain, forming a vertically-alternating pattern of "three-layer structure" and "dual structure". (2) The sand-mud ratio during normal lacustrine regression affects the contact relationship between the distributary channel-mouth bar complex and the main distributary channel, as well as the macroscopic morphology of the delta. Compared with the silt-rich delta, the shale-rich delta has the characteristics of "large scale, wide extension and node development". (3) Affected by the morphological characteristics of deltas, compared with silt-rich deltas, the sand bodies of shale-rich deltas extend farther but are relatively isolated, have poor connectivity, and are more closely related to source rocks. The alternation of normal and forced lacustrine regression enhances the heterogeneity of sand bodies.