Abstract: Ditches serve as important pathways for phosphorus transport into rivers and lakes and act as interception systems for reducing phosphorus loading to receiving waters. To evaluate the phosphorus control efficiency of combined treatments, sediment samples collected from three typical ditches in the Datong Lake basin were used to construct simulated ditch systems. Four treatments were established: control (CK), Myriophyllum aquaticum (P), 5% Ca(OH)₂-modified bentonite (M), and the combined treatment of M. aquaticum and modified bentonite (P+M). Static experiments and dynamic experiments with hydraulic retention times (HRTs) of 12 h and 6 h were sequentially conducted for 63 days. The results showed that the overall phosphorus concentrations in the water column followed the order of P+M < M < P < CK. On day 21, the concentrations of total phosphorus (TP) and phosphate phosphorus (PO₄^3--P) in the P+M treatment decreased to 0.136～0.169 and 0.083～0.114 mg/L, respectively, representing reductions of 58.39%～68.34% and 70.14%～75.68% compared with CK. Under an HRT of 12 h, the P+M treatment maintained relatively low and stable phosphorus concentrations during the later stage, with TP and PO₄^3--P concentrations of 0.118～0.152 and 0.053～0.102 mg/L, respectively, on day 42. When the HRT was shortened to 6 h, phosphorus concentrations increased, but TP concentrations at day 63 were still reduced by 55.94%～59.32% compared with CK. Meanwhile, the combined treatment resulted in the lowest levels of sediment available phosphorus and degree of phosphorus saturation.The combined treatment maintained effective phosphorus control even when both plant and material application rates were reduced by half, which may be attributed to the complementary functions of rapid phosphorus immobilization by modified bentonite and continuous phosphorus uptake by Myriophyllum aquaticum. Differences among HRT stages should be interpreted considering cumulative phosphorus loading and operational history. This study provides a reference for phosphorus control and process optimization in ditches of plain lake regions.