In order to solve the problem of velocity profiles in estuarine and coastal areas often deviating from the traditional logarithmic velocity distribution, a momentum exchange coefficient is derived based on log-linear velocity distribution, and an equation describing the vertical distribution of sediment concentration is established based on the diffusion theory. Through validation using measured data regarding vertical stratified sediment concentration in the Yangtze Estuary and Jinshan sea area in Hangzhou Bay, it is found that the new equation describing the vertical distribution of sediment concentration not only overcomes the Rouse equation defect of the surface sediment concentration being zero, but also agrees with the measured sediment concentration along the vertical line, indicating that the equation objectively reflects the vertical distribution rule of sediment concentration in estuary and coastal areas.