The utility model relates to a novel grassed swale experimental device. The system sequentially comprises a runoff input part, a water distribution part, a runoff transmission part and a runoff collection part, wherein the runoff input part comprises a circulating water tank, a circulating pump, a water pipe and a water inlet tank; the water distribution part comprises multi-point distribution water distribution pipes; the runoff transmission part comprises a trapezoidal groove and a supporting frame, the supporting frame comprises a first support, a second support and a lifting screw, and thefirst support and the second support are located at the two ends of the trapezoidal groove respectively; the runoff collecting part comprises a water outlet tank and a drain pipe. According to the novel grassed swale experimental device disclosed by the utility model, the grassed swale enters the trapezoidal groove in two paths, so that the uniformity of runoff distribution in the trapezoidal groove is good, and the accuracy of subsequent water quality testing is ensured; by adjusting the structure of planting soil, the section form is changed, and the hydraulic characteristics of different section forms are investigated; by adjusting the height of the lifting bolt, the inclination angle of the trapezoidal groove is changed, and grass planting ditch contrast experiments with different gradients are conducted.