After the Three Gorges Dam operation, the systematic scouring response of the downstream riverbed has resulted in a heterogeneous coarsening pattern of bed sediment, accompanied by structural modifications to the longitudinal replenishment mechanism of bed sediment for suspended load. Based on measured hydrological and sediment data from the Zhicheng, Shashi, and Jianli hydrological stations between 2003 and 2019, this study adopts Markov chain theory to develop a new formula for calculating sediment transport capacity that incorporates transition probabilities. This formula is then used to analyze suspended sediment concentration and cross-sectional erosion and deposition in the Jingjiang Reach below the Three Gorges Dam, revealing the changing characteristics and influencing mechanisms of suspended sediment transport in this reach after the reservoir"s operation. The results show that: (i) using a three-dimensional sediment transition probability matrix, a new formula for calculating the sediment-carrying capacity of cross-sections in the Jingjiang Reach of the Middle Yangtze River has been developed. The new formula demonstrates higher predictive accuracy than traditional formulas, with Nash-Sutcliffe efficiency (NSE) coefficients exceeding 0.716 at all stations; (ii) suspended sediment transport is predominantly concentrated during the flood season. The proportion of flood season sediment transport decreased from 98%, 93%, and 90% in 2003 to 93%, 87%, and 77% in 2019 at Zhicheng, Shashi, and Jianli stations, respectively, indicating a more nonuniform intra-annual distribution of sediment transport; (iii) under unchanged other conditions, the sediment transfer probability (P13) increases with flow discharge but decreases rapidly with increasing bed sediment grain size, approaching zero when the grain size exceeds 5 mm. When sediment concentration is below 0.2 kg/m3, P13 increases rapidly and then stabilizes; (iv) between 2003 and 2019, a positive correlation was observed between the sediment transition probability P13 and sediment transport rate. At the Zhicheng cross-section, P13 decreased from 0.469 to 0, while at Shashi and Jianli, it declined from 0.691 to 0.496 and from 0.789 to 0.742, respectively, reflecting a reduced capacity for suspended sediment supply due to bed coarsening in the reaches closer to the dam. The findings of this study provide a theoretical foundation for analyzing water-sediment transport and channel evolution in the near-dam reaches of the Middle Yangtze River.