A sodium alginate-gelatin based biochar multivariate composite material, a preparation method therefor and a method for removing cadmium in water body are provided and relate to the technical field of biochar adsorbent materials. The sodium alginate-gelatin based biochar multivariate composite material has a high and stable removal efficiency for cadmium divalent cation (Cd2+) in a potential of hydrogen (pH) range of 4-7 in the water body, with a maximum adsorption capacity of 86.25 (milligrams per gram) mg/g. The composite material of the disclosure has good recyclability. After five regeneration tests, the adsorption capacity of the composite material for Cd2+ can still reach 70% of the initial adsorption capacity. The preparation method of the disclosure has simple process, easy control, low manufacturing cost, and is suitable for large-scale production and application.