The invention provides a multi-reactor cascade pH value optimization control method in a metallurgical process. For the problems of many influence factors of calcine addition amount, ion test hysteresis and difficult control of calcine addition amount due to frequent change of working conditions and the like in the metallurgical process, the method is characterized by, through entry working condition division, by utilizing ORP and pH values obtained through on-line detection, and through combination of information of inlet solution flow, Fe2+ concentration and Cu2+ concentration and the like,establishing a calcine addition amount optimization control model according to export solution ion concentration, and obtaining a pH set value; and establishing a calcine adjustment amount correctionmodel based on fuzzy control rules to carry out correction on the current calcine addition amount to enable the pH value to reach an optimal set value, thereby ensuring stable operation of goethite inthe Iron precipitation process.