The reaction mechanisms for diesel soot oxidation over V-4/ZrO2 or V-4/TiO2 oxide catalysts were studied by the means of in-situ UV-Raman spectroscopy. The results indicate that the formation of surface oxygen complexes (SOC) is a key step and the SOC species mainly exist as carboxyl groups. The presence of NO in the reaction gas stream can promote the formation of SOC species. For soot oxidation over V-4/TiO2 catalyst, NO2 can be produced and remarkably accelerate soot oxidation. Based on the UV-Raman experimental results, two different reaction mechanisms are proposed for soot oxidation over V-4/ZrO2 or V-4/TiO2 samples, respectively.