pH is the key factor to affect reaction process. Adsorption and redox take place at pH > or =4 and pH <4, respectively. Free-radical and Mn3+ was inferred to produce and participate in reaction at pH <4. The oxidizing products of phenol are p-benzoquinone and biphenol determined by GC-MS. The efficiency of phenol and soluble manganese as a function of time and temperature were examined at pH <4 in order to test the mechanism inferred. Results show removal percents of phenol increase from 65% to 95% with time varied from 10 min to 70 min, but soluble manganese changes little. Removal percents of phenol increase with temperature also, but soluble manganese doesn't change. This means fresh manganese dioxide is not the only oxidant in aqueous and other oxidant , i.e. Mn34+, appears during the reaction. High valence cation, i.e. Al3+, promoted the removal percent of phenol while anion, i.e. PO4(3-), decrease the efficiency of phehol.