Abstract: Numerical simulations of a vertical flow desilting tank are conducted to explore how to improve its flow and silt concentration conditions by installing a set of slanting plates. This paper focuses on an analysis of the effect of slanting plates on its working efficiency and lays a theoretical basis for optimizing its flow structure and desilting efficiency. A mixture model and RNG k-??model are adopted to numerically simulate the flows, and the flow patterns and silt concentration distribution are compared with those modified by the slanting plates. Generally, in the unmodified tanks exist vortices that increase the turbulent kinetic energy and cause an upward movement of the suspended silt. The slanting plates, via improving flow structure, can prevent the vortex zone from extending further upward and hence impose a great influence on desilting efficiency. Such a tank design can effectively avoid the occurrence of turbid water density current at initial water filling stage, so as to improve the overall flow patterns in the tank. Another benefit from adding these plates is a significant improvement on the water quality of the tank outflow as a result of an increase in the silt precipitating area, along with the upward silt transport blocked by them. Thus, this study offers evidences of better flow structure and higher working efficiency of the desilting tank with slanting plates.