The work aims to investigate corrosion situation of reinjection water treatment system in gas processing plant in northern Shaanxi, and guarantee safe production of the system. The 20# and L316 steel on the site were used to study the corrosion situation of the system on the basis of water quality analysis. Water sample in the cycle subject to worst corrosion was selected as the medium. Effects of temperature, pH, dissolved oxygen and bacteria on corrosion rate of 20# steel were investigated in static weight-loss method. Total salinity of water produced from a gas field in northern Shaanxi was high (about 30 000 mg/L), so was content of metal cations including Ca2+ and Mg2+. The corrosion rate increased as dissolved oxygen content increased, and the corrosion rate was up to 0.4001 mm/a at 80 ℃ provided with 5.07 mg/L DO. The corrosion rate increased from 0.1065 mm/a to 0.2155 mm/a while the TGB increased from 60 cfu/mL to 6×104 cfu/mL, and SRB from 6 cfu/mL to 6×103 cfu/mL as bacteria content and corrosion rate increased. The corrosion rate decreased from 0.3039 mm/a to 0.0710 mm/a as pH value increased from 5.9 to 8.50. Corrosion of the system can be reduced by taking appropriate anticorrosion measurements including pH adjustment, sterilization and oxygen isolation.