A hydrodynamic cavitation device was applied to increase the acenaphthene amount in creosote oil. In the presence of FeSO4 and H2O as an inducer and initiator, respectively, effects of H2O amount, Fe2+ loading and pH of FeSO4 solution were investigated by mean of the orthogonal experiment method, and effects of cavitating reaction temperature as well as the height of cavitator immersing in the feedstock by single factor method. The result indicated that the maximum increase was 7.06 percentage points under the optimum conditions as follows: H2O amount 17.5% by the volume of feedstock, Fe2+ loading 0.3% by weight of feedstock, pH of FeSO4 solution 1, the terminal temperature T of cavitating reaction 75°C, and the immersing height of cavitator H 105mm. Based on the change trend of components in creosote oil the reaction mechanism was derived, and the validity of derivation process was confirmed by the material balance.