The invention discloses a preparation method of a stainless steel composite plate for a TMCP bridge; and the stainless steel composite plate for the bridge with excellent metallurgic bond is prepared through such steps as blank selection, surface treatment, isolating agent brushing, blank assembly, electronic beam sealing and welding, heating, rolling, straightening, cutting and plate separation. The preparation method adopts electronic beams to directly seal and weld under vacuum chamber environment, reduces such procedures as drilling and vacuumizing in a traditional process, and preferably guarantees the vacuum degree. The TMCP process guarantees excellent mechanical performance of substrate bridge steel and quick cooling after rolling, controls intercrystalline separation of coating materials, and guarantees excellent corrosion resistance of the coating materials; a substrate adopts a low-carbon designed blank; the prepared composite plate is low in carbon equivalent of the substrate, excellent in welding performance and convenient for scene construction; and in addition, the composite plate needs no heat treatment, and can obtain excellent comprehensive performance.