Sediment transport capacity (T-c) is a crucial parameter for understanding soil erosion and developing soil erosion models. Theoretically, an inflection point may emerge once the influence of soil particle size characteristics on T-c attains its utmost or least impact as slope (S) and flow discharge (Q) increase; however, few studies have explored the critical soil particle size characteristics that impact the mechanism of S or Q on T-c. In this study, T-c was analyzed for four soils (sandy loam, silty clay, silty loam, and silt) on the Loess Plateau at four Q (0.05, 0.07, 0.09, and 0.11 m(2) min(-1)) and five S (15.84 %, 21.26 %, 26.79 %, 32.49 %, and 38.39 %). The results revealed that silty clay exhibited the highest T-c. Both the S and Q significantly influenced T-c in all four soils (P < 0.01). S exerted a greater impact on T-c than Q for silty loam, whereas the opposite was observed for sandy loam, silty clay, and silt. Median particle size (D-50), sorting coefficient (sigma), and kurtosis (K-g) showed significant correlations with T-c (P < 0.01). The critical S and Q levels reversing the trend of the effect of D-50, sigma and K-g on T-c were determined as 26.79 % and 0.09 m(2) min(-1), respectively. Critical values of 26.72 mu m, 1.33 Phi, and 1.26 Phi were identified as the thresholds for D-50, sigma, and K-g, respectively, reversing the trend of the contribution of S and Q to T-c. These findings contribute to the theoretical understanding of sediment transport on the Loess Plateau.