The research on the normalization of the position and width-to-depth ratio of the grid flocculation tank top layer grid is blank. Using the FLUENT software, the standard k-ε turbulence model was employed to simulate the effects of inlet-to-first grid layer distance (h1) and width-to-depth ratio on the flow field in the grid flocculation tank. The CFD model was first verified by experiments, which showed that the average residence time distribution error was 3.03%, indicating that the numerical model was reliable. The CFD simulation shows that, when h1 ranges between 400 and 800mm, the dead zone in the flow field was small and the velocity distribution was relatively uniform, which provided good hydraulic conditions for floc particles to aggregate and collide. When the width-to-depth ratio of single tank was about 0.29, the vortex velocity gradient G′ was about 26 s-1, which is conducive to the formation of lots of dense flocs, and the crushing phenomenon is not easy to occur. This research provides a theoretical basis to some extent for the structure design in a grid flocculation tank.