The total installed capacity of the four cascade hydropower stations in the lower reaches of the Jinsha River is equivalent to two Three Gorges reservoirs. They are the source project of the central region of the "west to East power transmission". The benefits of the project are of great significance to economic and social development. Since 2012, Xiangjiaba, Xiluodu, Wudongde and Baihetan power stations had successively stored water and operated to intercept the sediment of Jinsha River layer by layer. From 2013 to 2020, the average annual sediment discharge from Xiangjiaba decreased to 1.52 million tons, a decrease of more than 99%. A large amount of sediment was deposited in the cascade reservoirs and scoured to the river channel below Xiangjiaba. Based on the observation data since the preparation of the lower Jinsha River project, this paper studied the sediment deposition of cascade reservoirs and the scouring law of the river channel downstream of the dam. The results showed that from the completion and operation of the four cascade hydropower stations in the lower reaches of Jinsha River to the end of 2020, the accumulated sediment deposition was about 598 million m³, of which the sediment deposition in Xiluodu Reservoir accounted for 92.5%. The sediment discharge ratios of Xiluodu and Xiangjiaba reservoirs from 2013 to 2020 were 2.64% and 22.2%, respectively. The reservoir sediment was mainly deposited in the main stream channel of the perennial backwater area, mainly in the dead storage capacity, and the proportion of occupying the effective storage capacity was less than 1.3%. The canyon characteristics of the main stream channel in the reservoir area of the lower reaches of Jinsha River were obvious, and the siltation was mostly the flat siltation of the main channel. The sediment deposited in Xiluodu and Xiangjiaba reservoir areas had obvious sorting characteristics along the way. The closer to the front of the dam, the medium particle size decreasd, the percentage of fine sediment increased, and the very fine sediment would be deposited in a large amount in a certain range of the reservoir area. The downstream riverbed of Xiangjiaba was generally scoured, but the scouring intensity was weakened obviously. The thalweg high convex section of the downstream channel of Xiangjiaba was relatively stable, so that the low water level at the downstream of the dam had not decreased significantly, and the cumulative decline of the low water level at 2000 m³/s was about 0.43 m. The riverbed at the downstream of the Xiangjiaba dam was obviously coarsened.