The invention relates to a silicane self-crosslinked halogen-free flame retardant polyolefin foamed composite and a preparation method thereof. The composite comprises a grated component A, a catalytic component B and halogen-free flame retardant masterbatch according to a weight proportion of 100: (3-10): (10-60), wherein the grated component A comprises low-density polyethylene, high-strength polyethylene, high-flow polyethylene, a silane crosslinking agent, a grafting initiator, a first antioxidant, a lubricating agent and 3-aminopropyl trimethoxy silane; the catalytic component B comprises an ethylene-vinyl acetate copolymer, low-density polyethylene, a second antioxidant, a crosslinking catalyst, a foaming aid and an ultraviolet light absorber; and the halogen-free flame retardant masterbatch comprises an ethylene-octylene copolymer, a modified main flame retardant, an auxiliary flame retardant, zinc stearate and a third antioxidant. The silicane self-crosslinked halogen-free flame retardant polyolefin foamed composite has the characteristics of excellent flame retardance, low smoke and toxicity, uniformity in foaming, natural crosslinking property, high temperature resistance and the like.