Abstract: Underground coal gasification (UCG) is consistent with the development of low-carbon green transformation of energy in China. However, the groundwater pollution caused by it is the bottleneck preventing from the promotion and application of UCG. Permeable reaction barrier (PRB) is one of the research hotspots for in-situ groundwater remediation. In this paper, combined with the characteristics of UCG with shaft, the influence of PRB’s thickness and purification materials on the migration and dispersion of organic pollutants in groundwater, and purification and remediation were investigated by numerical simulation. On the foundation of the advection-diffusion equation (ADE), two hypotheses were introduced: ① The mass transfer involved in the adsorption and purification of pollutants in groundwater is related to: (i) the difference potential between the concentration of pollutants adsorbed in the liquid and solid phases, (ii) the difference potential between the current adsorption concentration of solid phase and the potential maximum adsorption concentration, and (iii) the process time; ② The strong adsorption ability of activated carbon may lead to the gradual accumulation of adsorption concentration in the solid phase and no longer easy desorption with the change of the external liquid phase concentration. Both the migration of pollutants and the adsorption and purification processes were simulated numerically and validated experimentally after that the finite element method and \theta -format iteration were adapted and the corresponding program were coded in MATLAB. The results show that the remediation is enhanced with the increase of the thickness of PRB, but at a declining acceleration, and the marginal effect of the wall thickness increase on the purification shows the diminishing trend. The stronger the adsorption and purification rate of the wall material is, the better the purification of the PRB on pollutants will be, and the adsorption and purification rate also shows a diminishing trend of marginal effect on the purification. There is a synergistic influence between the thickness and the adsorption activity of the material, thus the thickness of PRB should be determined reasonably according to the adsorption and purification rate of the material when constructing PRB in order to obtain the best technical and economic consequence.