The invention provides adhesive of underwater repair of a steel structure and a preparation method of the adhesive, which belongs to the technical field of adhesives. The adhesive is prepared fromthefollowing components in parts by mass: 2 to 6 parts of nano silicon dioxide, 90 to 110 parts of biphenol A-E 51 epoxy resin, 10 to 15 parts of diluting agent acetone, 20 to 25 parts of double-quick cement, 50 to 55 parts of silica powder, 0.5 to 2 parts of wetting flatting agent, 40 to 50 parts of 1085A underwater curing agent, 30 to 35 parts of light calcium powder, 10 to 15 parts of talcum powder, and 1 to 2 parts of adhesive force accelerant. The underwater composite adhesive prepared in the invention is excellent in underwater composite adhesive construction and underwater curing performance and good in mechanical performance and has certain reference value for the reinforcing and repairing engineering of the underwater steel structure.