The invention discloses a geogrid pull-out test device for simulating a flexible top boundary. The geogrid pull-out test device comprises a drawing box placed on a bearing platform, a transverse groove is formed in the side wall of the drawing box; the geogrid horizontally extends into the drawing box through the transverse groove and divides the drawing box into an upper cavity and a lower cavity, the upper cavity and the lower cavity are respectively filled with soil, a rotatable rigid loading mechanism with a flat and smooth bottom surface is arranged at the upper end of the soil in the upper cavity, a support frame is constructed on the bearing platform, a pressurizing mechanism is suspended on the support frame, and the output end of the pressurizing mechanism is vertically propped against the upper end of the rigid loading mechanism. According to the invention, the rigid loading mechanism is rotatable; the phenomenon that in the test process of simulating the flexible top boundary through an air bag or a water bag, under the high pressure, the limit pressure bearing value of the air bag or the water bag is exceeded, and pressure explosion occurs is avoided, the process of simulating the change rule of the reinforced soil interface characteristics is more accurate, and the geogrid drawing characteristic of the flexible top boundary is simulated.