Abstract: For the displacement constraints of structural optimization problems, the threshold parameter of key constraints is introduced. A reduced-formula of unified displacement constraint is proposed to simplify the structural optimization model. According to the characteristics of structural optimization with discrete variables, the concept of efficiency coefficient is proposed to measure the effect of design variables’ variation in discrete neighborhood on cost function and constraints, and four adjusting modes in terms of the efficiency coefficient are analyzed. Based on the influence domain of stress and displacement constraints, an optimum synthetic effectiveness algorithm for structural optimization with discrete variables is proposed under the guidance of maximum synthetic effectiveness. From the analysis of numerical examples, it is indicated that the optimal solutions or best records can be obtained with high optimization efficiency by the presented algorithm.