In order to study the initiation law of consolidated cohesive sediments in Poyang Lake, the incipient velocity of cohesive fine sediment under different deposition duration and water depth was measured in a glass flume. Through a series of experiments on incipient motions after the deposition and consolidation, the variation laws of incipient velocity affected by the deposition duration and the water depth were found. According to the test data, the empirical formulas for the incipient motion, deposition duration and water depth of Poyang Lake sediment were obtained by fitting process, and the test results were compared with the calculation results of empirical formulas for the sediment incipient motion in the relevant literature. The results show that the consolidation degree of cohesive sediments in Poyang Lake went through four stages as the duration of sedimentation increases: the new sedimentation, the initial consolidation, the accelerated consolidation, and the stable consolidation. There was a positive correlation between the incipient velocity and the water depth. Meanwhile, the incipient velocity of sediment deposited for one-day was close to the result calculated by the empirical formula, the longer the deposition duration, the greater the difference between test results and empirical formula calculation results.