The corrosion inhibition of cold rolled steel (CRS) in 7.0 mol.L-1 H2SO4 solution by red tetrazolium (RTZ) was carefully investigated using both experimental procedures and theoretical techniques. The results show that RTZ acts as an effective inhibitor for the corrosion of CRS in 7.0 mol.L-1 H2SO4, and the maximum inhibition efficiency is higher than 95% with a RTZ concentration of 2.0 mmol.L-1. The adsorption of RTZ on CRS surface follows Langmuir isotherm. RTZ effectively retards both cathodic and anodic reactions, and acts as a mixed-type inhibitor. EIS exhibits two capacitive loops, and their resistances increase drastically in the presence of RTZ. SEM and AFM confirm that the addition of RTZ could significantly retard the corrosion of CRS surface. A series of characterizations like FTIR, RS, XRD and XPS reveal that the corrosion CRS surface is composed of the corrosion products of iron sulfates, iron oxides and iron hydroxide, as well as inhibitor. Theoretical results of quantum chemical calculation and molecular dynamics (MD) indicate that the adsorption center of RTZ(+) (organic cationic part of RTZ) mainly relies on its tetrazole ring, and the adsorption of RTZ(+) on Fe (001) surface is in a nearly flat orientation mode. (C) 2018 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.