Coastal salt marsh wetland is an important coastal ecosystem, and its geomorphic form and vegetation pattern are significantly affected by tidal dynamics and sediment supply. In recent years, research on the ecological and geomorphic dynamics of salt marsh has become a frontier research hotspot. Based on the dynamic environment of a typical salt marsh in China, a dynamic coupling model was established to study the vegetation-geomorphic coupling evolution of salt marsh wetlands under the influence of key variables such as tidal range, sea level rise rate, sediment supply, and sediment properties. Results show that the external sediment supply is the key factor to control the elevation and vegetation range of tidal flat and salt marsh. The higher the suspended sediment concentration, the slower the slope of flat surface, the higher the elevation of flat surface, and the wider the seaward extension of vegetation; the lower the sediment settling velocity, the more convex profile is formed, and the wider the distribution of wetland vegetation. The tidal range affects both the lower and upper boundaries of the salt marsh in the intertidal zone, and the larger tidal range and stronger tidal hydrodynamic forces favor the formation of higher tidal channel density and the transport efficiency of sediment to the salt marsh. This study provided a theoretical reference for coastal wetland protection and restoration projects.