The residual concentration of gemini quaternary ammonium salt was determined with the color reaction method using thymol blue as color developing reagent. The optimal developing conditions was obtained as follows, the concentration of color developing reagent was 0.4%, the best dosage of buffer solution was 10 mL, and the developing time was 60 min. The standard curve of absorbance and concentration of the?gemini quaternary ammonium salt solution was obtained to determine the concentration of the ?corrosion inhibitor. In addition, the influence of interference ions, polyacrylamide, and oil on test results has been studied. Tagged recovery rate of the method could reach up to about 98.6%, which could be generalized in the oilfield. The results showed that when the concentration of Ca²⁺ was below 4000 mg/L, the concentration of Mg²⁺ was below 1800 mg/L, or the concentration of Fe³⁺ was below 1.5 mg/L, the error of the testing method was less than 5%. When the concentration of PAM was below 200 mg/L, the relationship of absorbance and inhibitor’s concentration was linear. The crude oil in the sewage had a great effect on the testing results.