The environment-friendly hydrochloric acid pickling inhibitor was extracted from distiller's grains (DG). By comparing a variety of extraction methods of DG, the effect of different extraction method on inhibition efficiency of extraction was investigated, and the inhibition efficiency for Q235 steel in hydrochloric acid medium was studied by weight loss measurements, electrochemical measurements and SEM. The results show that the distiller's grains extract (DGE) acts as an excellent acid pickling corrosion inhibitor for the corrosion of Q235 steel in hydrochloric acid. The studies of inhibitor preparation methods show that the ultrasonic technology is the best method. The effective constituent of DGE is a mixed-type inhibitor in hydrochloric acid medium.