Abstract: Abstract: In this study, the objective aims at exploring the influence of biochar application on the rapid migration of 3,5,6-trichloro-2-pyridinol (TCP), the main degrading product of the wide-spread insecticide chlorpyrifos and the herbicide chlorophyll in purple soil where the large pore and preferential flow exist widely. Considering these objectives, a control group experiment with a series of biochar application ratio of 0, 1% and 2% (mass content) was designed. Above all, the isothermal adsorption experiment was used to analyze the change of adsorption capacity after the application of biochar with different ratios. Then the influence of biochar application on the soil structure and porous distribution were discussed on the basis of the reconstructed soil columns using the computed tomography (CT) scanning images. The breakthrough curve of TCP mixed the tracer of bromide ion was employed to analyze the effective degree of biochar application to reduce the migration of TCP. Finally, model establishment and parameter inversion were used to reveal the physical and chemical mechanisms of the reduction of TCP migration by biochar application. The results reveal that the application of biochar significantly changes the pore structure of the soil, which in turn changes the hydraulic properties of the soil and affects the migration of TCP. The pore structure of reconstructed soil based on CT scan has revealed that the application of biochar increases the total porosity of the soil, but reduces the soil's large porosity and average large pore diameter, while the pore shape factor also decreases. These changes reduce the movement rate, diffusion coefficient and the proportion of mobile water. When the application ratios of biochar are 0, 1% and 2%, the soil mobile water volume fraction are 31%, 27%, 25%, and the hydrodynamic diffusion coefficients are 2.15, 1.83 and 1.45 cm2/h, respectively. The reductions of these parameters significantly delay the time that contaminants enter the water body. The adsorption of soil on TCP increases significantly after the application of biochar. In the isothermal adsorption experiment, the Kf values are 0.80, 0.99 and 1.03 mg1-nLn/kg, corresponding to the ratios of biochar application (0, 1% and 2%). In the breakthrough curve experiment, the peak concentrations of the outflows are 0.82, 0.55 and 0.39 after a continually inputting 1 PV TCP, and the reductions of peak concentrations are about 31.40% and 52.44% with application of 1% and 2% of biochar in the soil, respectively. The parameters from the inversion simulation indicate that the soil adsorption characteristics, including the retardation factor R, the fraction of adsorption sites f and first-order mass transfer coefficient a, are significantly increased. Therefore, this study reveals that the biochar application effectively reduces the migration rate of TCP in purple soil, and initially uncovers the interacting mechanisms by changing soil pore structure, hydraulic parameters and adsorption dynamics, which are useful in agricultural non-point source pollution. However, limited by the resolution of the CT scanning images, the results only reveal the change of large pores (the diameter equaling to or larger than 267 mm). This study provides a reference for the control of agricultural non-point source pollution.