Objectives: Controlled by rivers and tides, the formation factors and development characteristics of tidedominated estuary reservoirs are complicated, resulting in difficult management of modern tidedominated estuaries and difficult prediction of ancient favorable oilbearing reservoirs. Methods: In this study, formation factors and distribution of sand bars in the modern strong tidedominated estuary —— Qiantang river were simulated and predicted by depositional numerical simulation, thus disclosing formation factors of sand bars in the estuaries and spatial distribution. Main controlling factors of sand bar formation factors and development characteristics in estuaries were studied by setting different bed dips and tidal energies using single factor analysis method.Results: Result demonstrated that: (1) The formation of sand bar in estuaries is controlled by tide. Sand bars in estuaries present zonal development characteristics. Near the estuary develop composite sand bar and Ushaped sand bar, river bars are mainly controlled by river hydrodynamic effects, and tidal effect is weak. Elongate bar is mainly the products of tide and distribute in the mid and outer estuary. The distribution of sandbar is similar to the Qiantang river estuary. （2） The tidal energy is enhanced, the tidal channel is widened and shallowed, and the Ushaped sand bar and composite bar developed on the estuary to the land side are eroded and cut into small sand bars, and the small sand bar on the sea side gradually evolves into an elongate sand bar; When the tidal energy becomes weak, the tidal sand bar is difficult to form. When the tidal energy is medium, the sand bar is relatively developed and has a continuous distribution trend. （3） With the gradual increase of the slope of the bed, the concentrated distribution area of the tidal sand bar gradually migrates to the sea, the differentiation of the sand bar increases, and the shape changes from an irregular point bar to a diverted sand bar, and the influence of the river is enhanced. When the slope of the bottom bed becomes smaller, the tendency of the sand bar to migrate toward the sea is weakened. At this time, the tidal action is enhanced, and the sand bar in the estuary area gradually evolves from an irregular point bar to an elongate sand bar, and the scale gradually becomes smaller. (4) The formation and distribution of sand bars are affected by the tidal energy and the bottom shape. Under the tidal energy M2: 2.5, S2: 2.1 and the bottom slope of 0.003°, the tidal sand bar develops and has a typical distribution of tidedominated estuary. Conclusions:The depositional numerical simulation method has been successfully applied to Qiantang River to reveal the sand bar formation mechanism and spatial distribution, the factors of the slope of river bed and tide energy are analyzed and under medium tide energy and slope will give a beneficial sand bar deposit which will later be a potential reservoir.