Abstract: Nitrogen gas injection in the third round of oil recovery is an effective way to improve recovery rate; however, scaling and corrosion bring serious oil development losses. The influence of injection agent on ground injection system and downhole strings was analyzed. The mixing of formation water and the low purity of nitrogen gas are the main causes for scaling and corrosion. We can reduce scaling and corrosion rates by using purer nitrogen gas, non-metallic materials and sacrificial anode materials.