The effect of Ti（Ⅳ）on the efficiency of acetic acid degradation by H2O2/O3 was investigated under acid condition. The processing parameters were optimized，and the degradation mechanism was also analyzed. The results indicated that addition of Ti（Ⅳ）could promote greatly the oxidation of acetic acid by H2O2/O3 at pH 2.8，the efficiency of its decomposition reached 52.0% in 30 min for Ti（Ⅳ）/H2O2/O3 and only 5.6% for alone H2O2/O3. When Ti（Ⅳ）and H2O2 concentrations were 6 mg·L-1 and 120 mg·L-1，Ti（Ⅳ）/H2O2/O3 had the highest degradation efficiency of acetic acid. The effect of pH was not significant，which might be related to the specific initiating mechanism for various pH values. In view of the shortcomings and characteristics of H2O2/O3，Ti（Ⅳ）/H2O2/O3 system that can be a complement to H2O2/O3 process，is suitable for application in acid solution. The test by using tert-butyl alcohol showed that acetic acid degradation in Ti（Ⅳ）/H2O2/O3 system followed a hydroxyl radical-type mechanism. The Rct values of H2O2/O3 and Ti（Ⅳ）/H2O2/O3 calculated by relative method were 5.548×10-9 and 2.128×10-7，respectively，indicating that Ti（Ⅳ）/H2O2/O3 system could generate more hydroxyl radicals.