Constructing a photocatalytic in-situ Fenton system (PISFs) is a promising strategy to address the need for continuous hydrogen peroxide (H 2 O 2 ) addition and the low efficiency of H 2 O 2 activation for hydroxyl radical generation in the traditional Fenton reaction. In this study, we constructed a photocatalytic in-situ Fenton system using anthraquinone-modified carbon nitride (AQ-C 3 N 4 ) for efficient pollutant degradation. The resultant AQ-C 3 N 4 not only enhanced the production of H 2 O 2 but also increased the generation of hydroxyl radical (·OH). Experimental results demonstrated that, the apparent rate constant for the degradation of 2,4-Dichlorophenol (2,4-DCP) by AQ-C 3 N 4 -PISFs was 0.145 min -1 , which is 2.74 times higher than that of C 3 N 4 under visible light. Density functional theory (DFT) calculations indicate that AQ modification promotes electron-hole separation while increasing the adsorption energy of O 2 . Independent gradient model (IGM) analysis based on Hirshfeld Partition revealed that van der Waals interactions between AQ-C 3 N 4 and 2,4-DCP promoted the degradation process. This work provides new ideas to overcome the problems of continuous addition of H 2 O 2 and low utilization of ·OH that exist in conventional Fenton system.