The invention discloses a solid-liquid separating device for drilling fluid based on fenders. The solid-liquid separating device comprises a casing, a feed opening and a discharge opening, wherein a desilting outlet is formed in a side wall of the casing; a first filtering plate is connected onto an inner wall of the casing through a hinge; a movable end of the first filtering plate penetrates through the desilting outlet; the height of a top surface of the desilting outlet is smaller than that of the hinge on the inner wall of the casing; a plurality of fenders are arranged on the first filtering plate; a plurality of springs are arranged below the first filtering plate; the lower ends of the springs are fixed on the bottom surface of the desilting outlet; a second filtering plate is horizontally arranged just under the first filtering plate. According to the solid-liquid separating device disclosed by the invention, under the action of gravity of water-based drilling mud, the desilting outlet is opened by means of gravity of solid phase particles stacked at the movable end of the first filtering plate while solid-phase separation is performed; discharging of the solid phase particles is realized, and the condition that the solid phase particles in the casing are discharged by using a spiral conveyor is avoided, so that the risk that an operator is injured is reduced, and application cost of the device is reduced.