This paper proposes an optimization design scheme for spatial steel frame structures based on the concept of "correlated discrete variables". By utilizing the calculation module of ABAQUS finite element software and its Python language interface, a plug-in is developed, therefore the optimization design of a spatial steel frame structures can be implemented based on its correlated discrete variables. Taking the total mass of a spatial steel structure as the objective function and the cross-sectional parameters of the components as design variables, the entire optimization design process can be quickly and conveniently completed under the premise of meeting structural reliability by using the plug-in. The optimization design results are obtained by searching the lower limit value of the total mass of the structure, which effectively saves the amount of steel used. The research has provided a good reference for structural optimization design and performance-based design of spatial steel structures, thereby promoting the intellectualization and economization of steel structure design.