Potentiodynamic polarization and impedance measurements are used to examine the effects of temperature on the passivation behavior and corrosion resistance of 13 Cr martensitic stainless steel in CO2 and Cl environment. Different specimens are tested during exposure to 90, 120 and 150℃. Reaction mechanisms are decided from polarization curves. The characteristics of the surface film are determined from impedance transfer function model, which involve the reactions occurring at the metal/passive film as well as diffusion processes. Information concerning system electrochemical parameters is used to interpret the effects of temperature on the passive film and corrosion resistance. These results are consistent with the SEM and XPS analysis.