Abstract: Dense medium separation is one of the most effective coal washing technologies, and its density loop control directly affects the efficiency of dense medium separation process. In this paper, a nonlinear PID switching controller is designed by considering the density loop of dense medium separation as the sum of the design model of the low order controller and unmodeled dynamics. Firstly, a Broad Learning System (BLS) is introduced to estimate the unmodeled dynamics, and the control error is introduced into the switching index. Secondly, the parameters are designed by a one-step ahead optimal control strategy, which realizes the stable tracking of the dense medium separation density. Finally, Experiments with actual data have been carried out on the density loop of dense medium separation, which shows the effectiveness of the proposed method.