By using five 110L simulated river reactors, the biostimulant dosage was designed as 0.08, 0.09, 0.10 and 0.11g/L, respectively, with adding aerobic denitrifiers (sediment and water were injected at a concentration of 0.09% and 0.03% of the agent), and the aerobic denitrifiers supplement group was used as a blank experiment, to study the repair effect in the collaborative effect of microorganism and biostimulant through more than 40days' experiment. The results showed that when the dosage of biostimulant was 0.10g/L, and the removal rate of COD in overlying water was 69%, which was higher than that of the other groups. NO₃^--N in the overlying water of each synergistic remediation group had no accumulation. The NO₃^--N removal rate is the highest at up to 0.11g/L, which is up to 96%; the TOC and TN content of sediments in each group did not change significantly within 40days. The TOC and TN removal rates of the sediment were significantly improved when the reaction time was extended to 84days. The urease activity of each collaborative group fluctuated, and the protease activity peaked at around 15d, with an increase of 106%~237%. Through high-throughput sequencing technology, the relative abundance of major functional groups, such as Desulfuromonas, Pseudomonas, Treponema_2, and Blvii28_wastewater-sludge_group increased at 43^rd day compared with the control group alone, and the biostimulant dosage was 0.10g/L can enable the microbial community to be more suitable for the degradation of nitrogen and organic matter in the direction of succession, effectively improving the sediment environment.