[Objective] The spatial distribution of the composition and contents of major element oxides in sediments along the Three Gorges reservoir was investigated in order to provide a scientific basis for sediment management in mountainous river-type reservoirs. [Methods] Taking sediments from the Three Gorges reservoir as the research object, riverbed and suspended sediment samples were collected, and their grain-size composition and contents of major element oxides were measured. The chemical index of alteration（CIA）, Na/K ratio(R_Na/K), Si/Al ratio(R_Si/Al), dealkalization coefficient（W）, and residual coefficient（I_K） were calculated to analyze the spatial distribution of sediment geochemical indicators along the reservoir. [Results] ① The sediments were dominated by fine particles, with average contents of silt, clay, and sand of 87.04%, 6.91%, and 6.05%, respectively. Overall, the sediments showed poor sorting, with skewness ranging from fine-skewed to symmetrical, and kurtosis mostly showing mesokurtic characteristics. From upstream to downstream, sediment grain size gradually became finer, and particle sorting became more evident.② Major element oxides in the sediments were dominated by the nonmetallic oxide SiO₂, followed by the metallic oxides Al₂O₃, Fe₂O₃, and CaO, while K₂O, MgO, and Na₂O were relatively low in content. In suspended sediments, CaO and MgO contents were slightly higher than those of Fe₂O₃ and K₂O. In terms of spatial distribution, SiO₂ and Na₂O contents showed decreasing trends along the reservoir, while Al₂O₃, Fe₂O₃, K₂O, and MgO gradually increased, and CaO showed no obvious spatial pattern. Compared with the upper continental crust（UCC）, the sediments were depleted in SiO₂, K₂O, and Na₂O but enriched in Al₂O₃, Fe₂O₃, CaO, and MgO.③ The sediments of the Three Gorges reservoir were in a moderate stage of chemical weathering under a warm and humid climate. The mean values of CIA, R_Na/K, R_Si/Al, W, and I_K were 73.26, 0.39, 5.25, 0.78, and 1.07 for riverbed sediments and 70.79, 0.68, 5.68, 0.94, and 0.85 for suspended sediments, respectively.④ Except for CaO, the contents of major oxides in sediments were significantly correlated with grain-size composition（p<0.05）. [Conclusion] The contents of major element oxides in sediments of the Three Gorges reservoir show distinct spatial differentiation along the reservoir, mainly influenced by factors such as the relative contributions of potential source materials and grain-size effects caused by hydrodynamic sorting.