Iron removal in the oil field produced water and effect of iron mass concentration in the outlet water on turbidity were explored by addition alkali process. Iron contents were determined by 1,10-phenanthroline spectrophotometry and portable turbidimeter was adopted at the determination of turbidity. Results show that pH of inlet water has significant effects on iron removal, turbidity reduce and anti-corrosion of treatment devices. Iron removal is bad and corrosion of treatment device could not be restrained when pH is below 7, which resulted in negative iron removal rate. Better pH is about 8.3 where iron removal and anti-corrosion of treatment devices are attained. And the quality of outlet water can meet the A1 quality standards of recommended indexes in SY/T5329-94 about the injection water quality for clastic rock oil fields, and its turbidity keep invariablenes at a dwell time of 2.5 h. However, outlet water turidity at 6.6 and 7.3 of pH rose gradually because of Fe(OH) ₂ oxidation. Coagulant can promote Fe(OH) ₂ settlement and major removal mechanisms of Fe(OH) ₂ include settlement, interception based on filtration and adsorption from theoretical analysis. At a low pH, electrochemical corrosion made treatment devices release iron which induces outlet iron contents above inlet iron contents. On the contrary, at a high pH, it is blockaded owing to protective layer formation and cathode reaction suppressed.