The invention discloses a method for establishing a stainless steel bar concrete mesoscopic numerical model. The method comprises the following steps: uncertain stainless steel bar concrete mesoscopicstructure composition, model establishment of each mesoscopic structure, constitutive relation of each mesoscopic component and determination of mesoscopic material parameters. Under the condition ofdetermining the mesoscopic material parameters of the coarse aggregate, the mortar, the mortar-coarse aggregate interface and the steel bar-mortar bonding interface, mesoscopic finite element analysis is carried out on the bonding performance of the stainless steel bar concrete. According to the method, based on a mesomechanics theory, detailed expression is carried out from the aspects of mesoscopic structure composition, constitutive relations of all mesoscopic components, determination of mesoscopic parameters, setting of boundary constraints and the like. A simplified method of a stainless steel bar solid structure in two-dimensional solid modeling is proposed, a parameter assignment method of a stainless steel bar-mortar matrix bonding layer microstructure material is studied, the influence of interface performance on bonding strength is analyzed, and the recommended value range of the tensile strength of a bonding layer is determined in combination with a calculation result.