Abstract: In this paper, the problem of large load fluctuation when the power closed-loop is input in the switching process of single sequence valve of Hollysys DEH system is studied, and the generation process of power loop and valve management logic is introduced. Through the establishment of mathematical model, theoretical analysis and data simulation, it is found that the valve flow management function of Hollysys DCS system is lack of sealing function, and a general conversion idea for analyzing complex problems is demonstrated.