［Objective］To improve painting efficiency and cut costs，while meeting the higherrequirements for dry film thickness of waterborne epoxy coatings in a single application within the steelstructure coating industry.［Methods］ Through the screening of waterborne epoxy curing agents， waterborne epoxy emulsions，and rheological additives，a high-build waterborne epoxy mica iron oxide（MIO） intermediate coating was developed. The study focused on the evaluation of the coating's sagging resistance，neutral salt spray test，pull-off adhesion，and continuous condensation test. Additionally，the water evaporation rate under different temperatures and wet film thicknesses wasmeasured via the mass loss method to determine the optimal application conditions.［Results］The optimized coating demonstrates exceptional application properties：sagging resistance of 425 μm（wet film，one coat），2 280 h neutral salt spray test，7 MPa pull-off adhesion，and 504 h continuous condensation test，meeting industrial requirements for heavy-duty corrosion protection.［Conclusion］ The composite coating system met all requirements for atmospheric corrosion category C4（H） as specified in the Chinese industrial standard HG/T 5176—2017（Water-based anticorrosive coatings for steel structures）. This work provides a reliable solution for industrial applications of high-performance waterborne epoxy intermediate coatings.