Radiolysis of p-chlorophenol (p-CP) was investigated through experiments and theoretical calculations. Its radiolytic intermediate products, i.e., phenol, hydroquinone, 4-chlororesorcinol, and 4-chloropyrocatechol, were identified using their mass spectra through a GC/MS system. Three transition states and a prereaction complex of the reaction between hydroxyl radical and p-CP were found from the density functional theory (DFT) study. Both the experimental and calculation results demonstrate that the main p-CP degradation pathway was the formation of 4-chloropyrocatechol.