The pollution of antibiotic resistance genes (ARGs) in marine environment has become a major challenge threatening human health and ecological security. Researches on biochar have mainly focused on the adsorption effect of single biochar materials on antibiotics in offshore environment, while relatively few studies have been conducted on biochar modified with mixed materials. Therefore, different raw materials (sawdust biochar, shell powder and attapulgite) were selected according to the ratio of 1:1:1, 1:2:3 and 3:2:1 to prepare functionalized biochar (FBCs), which were named FBC, FBC2 and FBC3, respectively. Batch adsorption experiments were carried out on sulfamethoxazole (SMX) and tetracycline (TC) using FBCs at different initial concentrations of antibiotics (1 mg/L, 5 mg/L). The results indicated that FBC1, FBC2, and FBC3 adsorbed 0.73 mg/g, 0.63 mg/g, and 0.59 mg/g of SMX solution at a concentration of 1 mg/L, respectively, which is 113%, 85%, and 74% higher than that of FBC (0.34 mg/g). At a concentration of 5 mg/L, the enhanced adsorption capacity of FBC1, FBC2, FBC3 was not significant as at 1 mg/L, but their adsorption capacity of TC was significantly higher than that of SMX (7.05–33.05 mg/g) (P < 0.05). This research offers theoretical backing and empirical validation for the creation of effective antibiotic adsorbents within marine ecosystems.