An understanding of the relationship between particle size composition and vertical hydraulic conductivity(K)of streambed is of importance to estimate streambed Kr accurately.By taking the middle seestion of the Weihe River as the research object,the Kr,values of streambed were derived by a falling-head standpipe permeameter test which was conducted at 43 locations of four sites along the river.Meanwhile,sediment samples in the locations were taken and particle size analysis of the samples was made.Then,the correlation between particle size composition and the Kr was analyzed.It can be concluded that the Kr,had a positive correlation with sand content and the ratio of sand to clay particles in sediment,while they had a negative correlation with clay particles.The regression equation for the relationship between particle size composition and the Kr, can provide reference for estimating the Kr,of streambed in the Weihe River by the particle size analysis.