Underground coal gasification (UCG) is a coal utilization technique that combines coal extraction and conversion. However, thepotential for groundwater pollution has emerged as a significant obstacle to its widespread acceptance and implementation. With the background of the UCG with shaft, phenol solution was used as the simulated UCG-contaminated water. Sand, a mixture of sand and organicbentonite, a mixture of sand and activated carbon were used respectively to construct the permeation reactive barrier (PRB). The finite element method and the Python scientific computing libraries, NumPy and SciPy were adopted to develop numerical inversion programs tostudy the breakthrough process of phenol in different PRB. The results show that: ① When the PRB was filled with sand and organic bentonite, the diffusion coefficient D and seepage velocity q increased, while the dispersion λ and retardation R decreased as the mass ratio ofsand and organic bentonite increased. Conversely, when the PRB was filled with sand and activated carbon, the diffusion coefficient D,seepage velocity q, and retardation R decreased, while the dispersion λ increased with an increase in the mass ratio of sand and activated carbon. ② The mass ratio of the mixed materials controls their porosity and adsorption capability, which significantly impacts theblockage and purification of phenol. When the PRB is constructed from sand and organic bentonite, increasing the mass ratio leads to anincrease in porosity and a shorter initial detection time for phenol. On the other hand, when the PRB is constructed from sand and activated carbon, increasing the mass ratio results in a decrease in porosity, and the initial detection time for phenol increases at first and thendecreases. ③ The adsorption and purification effect of a PRB on phenol and its mechanism can be explained as follows: in the case of aPRB material made up of sand and organic bentonite, there exists a threshold mass ratio (2 ∶ 1 in this experiment). When the mass ratiois below this threshold, the PRB effectively purifies phenol. However, when the mass ratio exceeds the threshold, the purification effectsignificantly decreases. On the other hand, in the case of a PRB material made up of sand and activated carbon, the dominant factor influencing the purification process is the seepage speed of the solution when the mass ratio of sand and activated carbon is below 2 ∶ 1. Conversely, when the mass ratio exceeds 2 ∶ 1, the adsorption performance of activated carbon becomes the dominant factor.