The invention provides a down-hole impact high-pressure jet grouting composite pile forming method. The method comprises the steps of S1, pile hole forming, S2, high-pressure jet grouting pile forming and S3, precast pile sinking and specifically comprises the steps that a down-hole hammer is driven by high-pressure air to impact and drill a formed pile hole, meanwhile, an ejector nozzle of a down-the-hole impact high-pressure jet-grouting drilling machine ejects high-pressure jet-grouting cement slurry to cut, stir and reinforce soil around the pile to form a uniform cement-soil mixture, and then a pile hammering machine or a pile static pressing machine is adopted to drive a precast pile with the diameter smaller than the diameter of the formed hole of the down -hole hammer into the bottom of the hole along the center of the high-pressure jet-grouting pile, therefore a composite pile is formed; the pile forming method can be applied to the aspects of foundation treatment, pile foundations, foundation pit supporting, waterproof curtains, elimination or reduction of foundation liquefaction, expansion and shrinkage of expansive soil and the like, has the advantages that the quality is stable and reliable, construction is convenient, the construction period is shortened, materials and construction cost are saved, and the manufacturing cost is reduced.