Abstract: Activated carbon has been widely used due to its good adsorption performance; however, the adsorption capacity is limited. Activated carbon was modified by ammonium hydrogen fluoride and nitric acid with a series of different concentrations. The surface chemical characteristics of pre-modified and post-modified activated carbon were analyzed by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrosocopy (FT-IR), Brunauer-emmett-teller (BET) Nitrogen Adsorption and Boehm Titration, and also their adsorption capability on Au(Ⅲ) was compared. The results showed that the ash, the specific surface area, pore volume and pore size of post-modified activated carbons decreased along with increasing concentration of nitric acid, which affected porous structure and reduced the absorption capacity. However, the quality of functional groups of hydroxyl and carboxyl dramatically increased. The polarity, hydrophilic, catalytic properties, surface charge and skeleton electron density of the activated carbon were improved, which increased adsorption selectivity and adsorption capacity for metal ions. The specific surface area, pore volume and pore size of activated carbon modified by 20% concentration of nitric acid had lower degree of reduction, but phenolic hydroxyl content and total oxygen functional groups were increased by 168.3% and 109.1%. Compared with pre-modified activated carbon, Au(Ⅲ) adsorption rates of activated carbon modified by 20% concentration of nitric acid had the largest increase of up to 99.1%. The precision range of Au determination was 0.6%-1.4% with high accuracy. Adsorption on Au(Ⅲ) of post-modified activated carbon was the coexistence of surface physical adsorption and chemical adsorption of functional groups, and chemical adsorption played a main role.