Abstract: The mixture of 2-undecyl-N-carboxymethyl-N-hydroxyethyl imidazoline（UHCI） to KI as a corrosion inhibitor for carbon steel in 8 % amidosulphuric acid solution was investigated by weight loss test,electrochemical methods.Results show that the combined inhibitor strongly inhibits the corrosion of 45# carbon steel in amidosulphuric acid solution and the mixture with the mass ratio（UHCI:KI） of 9:1 has the best corrosion inhibition at a total concentration of 0.4 %.The impedance spectra of carbon steel electrodes change from one time constant into two time constants when the mixture inhibitor adds into the blank solution while the polarization curves indicate that the mixture behaves as a mixed type inhibitor.The absorption of the mixture is found to follow the Langmuir adsorption isotherm and the mechanism is chemisorption.