Abstract: In order to investigate the influence of acid treatment on the characteristics of coal in organic waste water treated with lignite, the brown coal in Mengdong was taken as the research object, and the coal samples were treated with different concentrations of hydrochloric acid and nitric acid solution. The changes of pore structure, surface functional groups and surface morphology of lignite before and after acid treatment were analyzed by BET, XPS and SEM. Results showed that with the increase of acid concentration, the specific surface area of lignite and the total pore volume first increased slightly, then decreased gradually. The average pore size of coal treated with higher concentration of hydrochloric acid increased compared with that of raw coal, while the average pore size of nitric acid treated coal generally decreased. The proportion of acid-treated lignite, C-C and C-O groups decreased, C=O groups increased, and the change after nitric acid treatment was more obvious. The homogeneity of particle size of lignite was improved and the folds were reduced after acid treatment at room temperature. The acid treatment changed the physical and chemical structure of coal to a certain extent, and the effect of nitric acid was more obvious than that of hydrochloric acid.