The invention discloses a composite bentonite material capable of quickly identifying hexavalent chromium ions in water with naked eyes as well as a preparation method and an application of the material. A core of the material is hydrophobic nano organic modified bentonite, wherein the core is connected with a color developing agent, namely diphenylcarbazide in a modifying manner through a hydrophobic carbon chain so as to form a novel composite bentonite material capable of identifying specificity of hexavalent chromium. The hydrophobic nano organic modified bentonite is prepared by modifying quaternary ammonium salt and has the characteristics that the content of montmorillonite is greater than 88%, cation exchange capacity is 80-130mmol/100g and the whiteness is 76-95. Through the composite bentonite material, the detection process is simple, no detection instrument is required, the cost is low, the labor intensity is low, no organic solvent is needed, the pollution to the environment is avoided, and the health of detection workers is guaranteed.