The invention discloses a method for preparing a fishing line from a sisal hemp fiber and polyethylene fiber composite material. The method comprises the following steps: immersing sisal hemp fibers into a hydrogen peroxide solution; immersing super-high molecular weight polyethylene fibers into a potassium permanganate solution; mixing to obtain mixed fibers; quickly freezing the mixed fibers by an instant freezer, and immersing the mixed fibers with a sodium acetate solution; quickly raising the temperature to obtain the mixed fibers subjected to primary treatment; preparing a modifying solution from methyl methacrylate, isocyanate, absolute ethyl alcohol, ethylene glycol and fatty acid methyl ester ethoxylate; treating the mixed fibers, and immersing the mixed fibers into 1-butyl-3-methylimidazole tetrafluoroborate ionic liquid to obtain the modified mixed fibers; mixing the modified mixed fibers, an enhancing agent, a toughening agent, a waterproof agent and an ultraviolet absorbent, and conveying a mixture into a banbury mixer; blending, and conveying a mixture into a line production machine to prepare the fishing line. By adopting the method disclosed by the invention, the fishing line which has good toughness, high strength, good compatibility and low cost and is prepared from a fiber composite material can be obtained.