The work aims to adopt middle layer of stannate conversion film to avoid the direct contact between electroless nickel plating coating and metal matrix, so as to reduce the trend of the galvanic corrosion and improve the corrosion resistance and stability of electroless nickel plating coating of magnesium alloy. The stannate chemical conversion film (SCC) was prepared on AZ31 magnesium alloy by stannate chemical conversion film technology and then the Ni-P coating was deposited on SCC layer by direct electroless nickel plating technology. The microstructure, phase composition and corrosion resistance of composite coatings were studied by SEM, EDS, Hydrogen Evolution Reaction test, electrochemical test, etc. The SCC film was composed of small uniform spherical particles, and there was a gap between the particles, which provided a possibility for the initial deposition of Ni-P alloy during the direct electroless nickel plating process. The electroless Ni-P coating deposited on the surface of the SCC film was uniform and dense with a typical cellular structure. The combination of matrix-chemical conversion film-electroless Ni-P alloy layer was good, which ensured the excellent corrosion resistance of the composite coating. The electroless Plating Ni-P coating can be deposited directly on the SCC film without palladium-activated treatment. The middle layer of the SCC film avoids the direct con-tact between the Ni-P alloy cathodic coating and the anodic magnesium matrix, reduces the influence of the local micro-defects of the Ni-P coating on the overall protection effect and improves the corrosion resistance and durability of the coating.