The invention discloses a deep foundation pit combination supporting construction method for geology with high water level and large particle size sand gravel. High pressure jet grouting pile construction is conducted outside a foundation ditch retaining and protecting system, by means of a triple placing method, cement paste is injected into underground soil filling layer and sand gravel gaps, after solidifying, secant pile wall and retention wall are formed, the underground water is prevented outside the periphery the foundation ditch retaining and protecting system, and conditions are created for the construction of a support pile; when the strength of outer side jet grouting pile meets design requirements, a long auger drilling cast-in place pile begin to be constructed close to the inner side of the jet grouting pile; after perfusion pile beings maintained for 15 days, jet grouting pile construction begins to conduct to make up partial failure of waterproof curtain of the jet grouting pile in construction of retaining and protecting pile, and retaining and protecting strength and water interception effect of the retaining and protecting system are increased; at last, in an earth excavation process, bar-mat reinforcement sprayed concrete slope protection and construction of dewatering well, open trench and water-collecting well in the foundation ditch are completed well, multiple retaining and protecting forms are used for combining construction and interaction. Accordingly, the problems of retaining and protecting the geology with high water level and large particle size sand gravel and processing the geology are solved.