Abstract: A distributed optimization problem is cooperatively solved by a network of agents, which have significant applications in many science and engineering fields, such as metallurgical engineering. For complex industrial processes with multiple-level characteristics, varying working conditions, and long processes, numerous optimization decision-making micro and macro control problems, such as product quality control, production planning, scheduling, and energy comprehensive deployment, are encountered. The theory and method of distributed optimization are keys to promoting the strategic decision-making of the integration of industrialization and new-generation industrial revolution. Their development enhances the ability to deal with large-scale and complex problems of big data, which have important practical value and economic benefits. In this study, consensus optimization with set constraints in multi-agent networks was explored. A distributed algorithm with a fixed step size was proposed on the basis of a primal-dual gradient scheme. Parameters such as step size affect the convergence of the algorithm. As such, convergence should be analyzed first, and appropriate parameters should be subsequently set in accordance with convergence conditions. Existing works have constructed different Lyapunov functions by exploiting the specific iteration scheme of this algorithm and analyzing convergence. Conversely, a convergence analysis paradigm based on a Lyapunov function was proposed in this study for general fixed step size iteration schemes, which were similar to the analysis method of Lyapunov convergence for general differential equations. A suitable Lyapunov function was constructed for the distributed gradient algorithm, and a parameter setting range was obtained in accordance with the convergence conditions. The proposed method avoids the tedious and complicated analysis of algorithm convergence and parameter assignment. The theory and method presented in this study also provide a framework and systematic demonstration method for other types of distributed algorithms and may be regarded as future directions of distributed optimization.