In the present study, we experimented the risk-free degradation of p-chlorophenol thinly dissolved in water with ozone and investigated the influences of adding CaCO3 and H2O2 as oxidation promoters on the behavior of producing organic acid components. In a simple ozone oxidation treatment, the degradation rate of p-chlorophenol was increased with increasing dissolved ozone concentration. However, the increased concentrations of hydrochloric acid and organic acid components reduced the degradation rates of p-chlorophenol and their degradable products including organic acids because the significant decrease in pH occurred, which might in turn restrained the generation of hydroxyl radicals in the solution. Addition of a small amount of CaCO3 helped to significantly recover the oxidation ability of dissolved ozone by maintaining the pH value in a range above or about 7 and could decompose the oxalic acid which would otherwise remain in a large amount in a simple ozone oxidation treatment. With additions of CaCO3 and H2O2, together, the degradation rate of p-chlorophenol was accelerated most, compared with the other cases of ozone treatments, the produced intermediate substances were quickly decomposed. The remaining organic acid components in small amounts resulted in sufficiently higher value of pH maintaining a promoting oxidation condition for generating a large amount of hydroxyl radicals supplied from added H2O2. It was found that the degradation rate of p-chlorophenol is first order with respect to its concentration and the apparent first-order reaction rate could be correlated with a power function of the dissolved ozone concentration at specified concentrations of additives.