Wastewater treatment of steel industries as one of the most important and water-consuming industries is of high important, especially in terms of wastewater reuse. One of the most important and newest methods for industrial wastewater treatment is the coagulation and flocculation method, in which the efficiency of the process can be greatly improved by controlling various factors such as temperature, pH, retention time and coagulation concentration. In this study, the efficiency of polyaluminum chloride in removing the turbidity of simulated hot-rolled effluent of a steel plant was evaluated in the presence of independent variables of pH, stirring time, temperature, oil concentration and suspended solids. The experiments were performed by Design expert 8 software. To do so, the central composite design method was applied as the most common type of design in the response procedure method. The results showed that increasing the polyaluminum chloride coagulant to about 5 mg / l increases the turbidity removal efficiency, thus reducing the turbidity to less than NTU 20, which is a standard for water turbidity used in the rolling process. Increasing the temperature from 27 to 55 degrees has slightly enhanced the turbidity removal efficiency. According to the test design results, the best turbidity removal efficiency from the studied effluent (51 to 62%) was achieved at polyaluminum chloride of 1 mg / l, the amount of suspended solids of 1500 mg / l and the stirring time of 30 seconds. In this case, the range of turbidity removal efficiency was. The results showed that pH, temperature and oil content had the lowest effectiveness. Overall, the results of the present study indicate that the optimal addition of polyaluminum chloride to the effluent improves the effluent turbidity removal.