This paper is concerned with the optimal control problem for the zinc electrowinning (EW) process during the current switching period. A mathematical model is developed to reveal the dynamic characteristics of the whole plant of the zinc EW process and an energy consumption model is established to set the expected set points of the concentrations of the zinc ion and the sulfuric acid under different current. Furthermore, an optimal control problem is constructed in the light of free initial time, free terminal time, and fixed system switching time during the zinc EW process. A novel time-scaling transformation-based control parametrization method is introduced to transform the optimal control problem into a multiple parameters optimization selection problem, which can be effectively solved by the optimization algorithm. The applications on the EW process of a zinc hydrometallurgy plant demonstrate the validity of proposed method.