Abstract: Systematic study on heterogeneous catalytic oxidation reaction of benzene to malcic anhydride over V_2O_5 catalyst by transient response method was made. In an isothermal integral reactor, through the combined step-up and step-down transient response experiment of benzene specifically designed, conclusion was reached that benzene in gaseous state takes part in the reaction, oxygen is adsorbed on the surface of the catalyst and some inter mediates are formed during the reaction.