Abstract: Using low temperature gas multi-component co-penetrated technique,C-N-O-Cr co-penetrated layer was obtained on the surface of N80 steel.The phase composition,morphology,thickness and the distribution of the co-penetrated elements of the co-penetrated layer were investigated by means of XRD,SEM and EDS.The polarization curve and the corrosion rate of the penetrated layer in the simulated saturated oilfield brine with carbon dioxide were tested.The results show that the thickness of the penetrated layer was about 70 μm.And the layer was composed of the 40 μm oxide layer with many Cr-O phase around the substrate,15 μm nitride layer with ε phase and γ′ phase near the oxide layer and the outmost iron oxide layer.To compare with the substrate,the corrosion potential of the C-N-O-Cr penetrated layer increased 320 mV in positive direction,the corrosion rate in the simulated saturated oilfield brine with carbon dioxide was only one-third of that of the substrate sample.