Abstract: Estimating pressure drop accurately is the key to develop and design spacer grids.Grid pressure drop prediction models are reviewed.Most of the empirical corrections applied for the pressure drop calculations do not contain any real geometrical parameter to characterize the grid effect.From the aspect of fundamental research,the influence of the dimple location,distance of the mixing vane to the nearest strip and the effect of inter-subchannel mixing among neighboring subchannels on pressure drop and downstream flow fields are analyzed using the commercial CFD codes.Based on this study,it is concluded that more detailed geometry parameters of spacer grid should be added into the correlation when predicting the pressure drop.Dimple location,configuration of mixing vanes and grid strip opening should be optimized for different design targets and functions when developing spacer grids.