The invention relates to a method and a reinforcing device for transverse limit and reinforcement of the middle part of a steel trestle, the limiting and reinforcing device comprises a first reinforcing steel pipe pile, the second reinforced steel pipe pile and the third reinforced steel pipe pile, slide block, The first reinforced steel pipe pile, the second reinforced steel pipe pile and the third reinforced steel pipe pile are triangular in distribution, and the third reinforced steel pipe pile is provided with two sliding paths at intervals on the outer surface of the third reinforced steel pipe pile. The sliding block is located between the two sliding paths, and the inclined support beam obliquely supports the upper part of the outer side of the third reinforced steel pipe pile. Thesteel trestle has the advantages of simple structure, low cost, strong applicability, stable and reliable performance, strong maneuverability and good use effect, and has the advantages of improving the overall rigidity of the steel trestle, enhancing the resistance to water flow and wind load.