The corrosion inhibitor has been widely used to mitigate the corrosion of carbon steel in oil and gas industry. The effective concentration of corrosion inhibitor inevitably decreases with the prolongation of its service time in oilfield environment, thereby affecting its anti-corrosion effect. It, thus, puts forwards an urgent demand for the residual concentration detection technology of corrosion inhibitor in oilfield. The primary objective of this study is to determine a feasible method used for the residual concentration detection of imidazoline corrosion inhibitor in oilfield. In this regard, the ultraviolet absorption spectrum and absorbance of imidazoline corrosion inhibitor were measured by ultraviolet-visible spectrophotometry in the solution with various salinity, pH and Fe3+ concentration. The effects of the salinity of the simulated formation water, pH and Fe3+ on the absorbance of corrosion inhibitor were investigated and meanwhile, how the above factors affecting the relationship between inhibitor concentration and absorbance were analyzed. The results show that the variation of the salinity of produced water as well as the presence of ions such as Na+, K+, Ca2+, Mg2+, Cl?, SO42? and HCO3? rarely affects the absorbance of corrosion inhibitor, which does not disturb the detection on the inhibitor concentration. However, the potential suspended substance in produced water has significant influence on the absorbance measurement of corrosion inhibitor. Therefore, the produced water needs to be filtered prior to the detection on inhibitor concentration. The change of pH in the range of 7 to 11 has no obvious effect on the absorbance of corrosion inhibitor while that in the range of 2.5 to 6 results in the fluctuation of absorbance within –0.02-0.02, which can cause the small detection error of about ±5 mg/L for the corrosion inhibitor. The influence of the possible Fe3+ in produced water on the absorbance measurement of corrosion inhibitor is very huge. It is necessary to eliminate the interference of Fe3+ on the absorbance measurement of corrosion inhibitor when conducting the inhibitor concentration detection on the produced water containing Fe3+. A feasible method to implement the residual concentration detection of imidazoline corrosion inhibitor in the formation water of oilfield is proposed as follows:taking the corrosion inhibitor sample to prepare at least two solution with different inhibitor concentrations, measuring the wavelength (λ) of characteristic absorption peak and the absorbance (A) to determine the relationship between inhibitor concentration and absorbance (A=kC); taking the produced water sample with unknown concentration of corrosion inhibitor; filtering the water sample; measuring the A of water sample at λ by means of ultraviolet-visible spectrophotometry; detecting Fe3+ and measuring its concentration (CFe3+); calculating the residual concentration of corrosion inhibitor (CR) according to the formula of CR=A/k in produced water without Fe3+ or determining CR according to the formula of CR=(A–0.056 5CFe3+)/k in produced water with Fe3+. The detection error of the proposed method is less than 10 mg/L in the inhibitor concentration range of 0-300 mg/L, especially the lower the residual concentration of corrosion inhibitor in the produced water, the smaller the errors of the detected results. This work provides a potential strategy for the residual concentration detection of corrosion inhibitor in the formation water of oilfield.