By means of flumes, experiments have been done in order to determine the effects of consolidation time and particle size on scour rates of cohesive sediment. Experimental results shown dry unit weight increased and scour rates decreased during the course of consolidation, the resistance to scour was related to consolidation time, but it presented different consolidation properties that depended on particle size. For the finer particle, the consolidation process was longer, the range of dry unit weight altered was greater, the consolidated sediments moved in chunks. On the other hand, based on analysis of the relationship of dry unit weight change with consolidation time, the simplified analytical expressions of dry unit weight and scour rates were derived, the results were checked with experimental data in the same flow situation and good agreements were achieved. Since the effects of different particle size were considered during the process of consolidation, the variations of consolidation properties were well reflected in these formulas.