Plant-wide optimization for a complex process consisting of multiple unit processes is an effective method to achieve production with high efficiency and low consumption. However, due to the complexities of the plant-wide optimization problem such as high dimensionality, numerous constraints, and other factors, plant-wide optimization for a complex process is always a challenging problem in research. Therefore, this paper presents a plant-wide hierarchical optimization method based on a minimum consumption model which can solve the feasibility and optimality of the obtained technical indices. The plant-wide optimization problem is converted into a two-level optimization problem, including the procedure-level optimization and the process-level optimization. The presented method can simplify the original plant-wide problem and effectively reduce the computational complexity. Moreover, the hierarchical decision-making is achieved simultaneously and the efficiency of solving the optimization problem and the global convergence is improved. Finally, the presented plant-wide hierarchical optimization method is applied to the hydrometallurgy process of a gold smelter. The results verify the effectiveness of this method.