The invention relates to a production process for an open pit tailings reservoir, and belongs to the technical field of tailings reservoir production process. The production process comprises the following processing procedures, namely magnetic separation of tailings, selective tailings filling, concentrating and discharging of tailings and internal drainage of the tailings reservoir. Through the improvement on the production process for the open pit tailings reservoir, production problems that a tailings discharge pipe network is easily jammed, the space utilization ratio of the reservoir bottom is low and the failure rate of water pumps in the reservoir is high are effectively solved, the production process is reliable, efficient in cleaning, low in investment, high in economic benefits, capable of prolonging the service lie of the open pit tailings reservoir and high in the comprehensive utilization ratio of mineral resources; besides, the improvement on the production process for the tailings reservoir can be carried out when open pits of copper sulphide ore, nickel sulphide ore and sulphide copper-nickel associated ore needs to be changed into tailings reservoirs.