We analyzed the behavior of catalytic fixed-bed reactor(CFBR) which synthesizing Phthalic Anhydride(PA) from air oxidation of o-xylene. The behavior of CFBR describing convection-diffusion-reaction mechanism was examined by using two-dimensional, transient, pseudohomogeneous model, for the kinetics of Arrhenius type. Prediction model was composed by optimum parameter estimation from best fitting on temperature profile and yield of dual CFBR which was measured in the industrial field. An uniform CFBR with same yield and conversion for dual CFBR generated a 36.15℃ higher hot spot temperature than a dual CFBR. We could predict parametric sensitivity according to the variation of possible operating condition of uniform CFBR and dual CFBR. Dual CFBR showed the behavior of wide operating range than uniform CFBR on the temperature, concentration, volumetric flow rate of feed reactant and coolant flow rate, thus, dual CFBR with nonuniform activities could assure safety operation condition by minute variation of operating condition.