Abstract: Based on the practical background that ecological water diversion can improve water environment, a Filippov dynamic model of nutrient phytoplankton is constructed. Firstly, the qualitative properties and stability of the subsystems are studied. It is pointed out that the subsystems may have a globally stable positive equilibrium point, respectively. Secondly, the sliding mode dynamics of the Filippov system, including the existence and stability of the real equilibrium point, the virtual equilibrium point, the pseudo equilibrium point and the tangent point, are discussed. Finally, the sliding bifurcations related to the boundary equilibrium point are given by theoretical analysis and numerical simulation, and the corresponding biological significance is given.