To precict the suspended sediments which are 80% of total sediments in a flood disch-arge, an equation representing vertical distribution of sediment concentration was derived based upon the diffusion theory and the logalithmic velocity distribution function in the tubulent flow mechanism. The hypothesis that the uniform mass transfer is occurred at upper part along the center line of water depth, was established as a preconition to solve the problem. The theorecal and the observed values were compared. And the theoretical equation was modified to be fit the theoretical values the observed values. Observed results are as follow; 1) Equation 12) is the theoretical equation representing the vertical concentration distri-bution of suspended sedimenta 2) Rous&exonential type vertical concentration distribution equation shows signification errors near the water surface. But the equation 12) shows substation cocentration values near the water surface. 3) Equation 15) is the modified theoretical equation which is possible to predict the vertical concentration distribution of suspended sediments.