The fire drive off-gas in Xinjiang oilfield contains three types of corrosive gases, namely O2, H2S and CO2.In the paper, 35CrMo steel is selected as experimental material.Orthogonal experiment is designed based on field working conditionsand the corrosion rate is studied by weight loss method.Aimed at typical conditions, corrosion product films are studied by SEM and the like.The findings reveal that general corrosion occurs on the 35CrMo steel under experimental conditions and the composition of gases exerts the greatest impact on corrosion rate,followed by temperature and total pressure in turn.Corrosion product is mainly granular, mixed with platelet when O2is contained.As partial pressure of O2and temperature increasing, corrosion rate become much higher, product film becomes thicker.There are four elements of Fe, C, O, S in corrosion product mainly, Cr was detected as well.Corrosion product consisted of sulfide of Fe and oxide of Fe and Cr.The reason is that besides precipitating in oxygen absorption reaction, O2also oxidizes some product such as Fe2+.Moreover, O2interacts with H2S, generating S, and with CO2, restraining formation of FeCO3.The findings provides research on corrosion mechanism and protection of metallic materials with theoretical basis under O2, H2S and CO2mixed system.