In order to study the tensile properties and constitutive relationship of heavy-dutyanticorrosive coating for steel structures，the uniaxial tensile test was carried out with long-lasting primer，intermediate paint，topcoat and composite coating as experimental objects. Theconstitutive expression of the coating was established by fitting the stress-strain curves in phaseswith the experimental data. Based on the experimental results，the mechanical performance parameters were determined. According to the rule of mixture，an expression was proposed topredict the tensile properties of composite coating by single coating，and uncertainty analysis was used to verify the reliability of the theoretical prediction. The results showed that heavy-duty anticorrosive coating for steel structures was typical plastic materials，the working process of the coating was divided into three stages：approximate elasticity，plastic strengthening anddestruction. The constitutive relation could be expressed in terms of a segmented functioncombining a linear function with a quadratic function. The elastic modulus of the intermediatepaint and primer was 54. 11 and 7. 22 times that of the topcoat，respectively，which was the main load-bearing part of the composite coating. The elastic modulus and tensile strength ofthe composite coating could be predicted by single coating with high accuracy.