The invention provides a polyurethane-coated hollow glass micro-bead toughened cast nylon 6 composite material preparation method, which specifically comprises: coating the surfaces of hollow glass micro-beads with a polyhydroxy raw material according to a certain ratio in a spraying manner, mixing with diisocyanate, carrying out in-situ polymerization on the surfaces of the hollow glass micro-beads at a proper polymerization temperature to prepare polyurethane-coated hollow glass micro-beads, intermittently adding lactam, the polyurethane coated hollow glass micro-beads, a catalyst and an activating agent into a reaction kettle according to a certain ratio, carrying out pre-polymerization activation, injecting the hot slurry with a certain viscosity into a hot mold, carrying out polymerization curing, and carrying out cooling demolding to prepare the composite material. According to the invention, hollow glass micro-beads are coated with polyurethane to toughen nylon, so that the toughness of the composite material can be improved on the premise of no reducing of the strength, the modulus, the rigidity, the hardness and the heat resistance of the composite material.