Abstract: The ions in the nature river would affect the fine sediment set ling velocity. But the sediment settling velocity formula could not reflect the influence before. So the formula could not compute the velocity of the sediment particle settling in the water with ions It is necessary to amend the formula to compute the velocity in this situation. The fundamental cause of generat ing influence on the settling velocity by ions is flocculation of fine sediment. And in this process the most importantions in river are high valency cations. Based on the analysis of sediments flocculation process,a empirical formula between the set tling velocity of the fine sediment flocculation and the ion concentrat ion is established. And the emcpirical relat ionship based on the experimentations is given. So the coefficients in the formula are confirmed by the experience of the sediment settling velocity in the distiled water and the water with different Ca²⁺ concentration. By taking account of the Zhang Ruijin formula and the empirical relationship formula,the sediment flocculation settling velocity formula about Ca²⁺ comes into being. The preliminary verification of the formula is made through the contrast between the actual measured value and computed one. The results of verification show that the results computed by the flocculation settling velocity formula are more rigorous than those done by the Zhang Ruijin formula.