The utility model discloses a sit-up gymnastic device, which mainly comprises a horizontal plate, a frame, a swing rod, an upper leaning foot, a lower leaning foot and an elastic pull rope, wherein the upper end of the swing rod is hinged on the upper end of a vertical bracket of the frame, and the middle part of the lower leaning foot is fixed at the lower end of the swing rod; the elastic pull rope is wound between the swing rod and the vertical bracket of the frame; and the horizontal plate is fixed on a longitudinal beam of the frame. Because the longitudinal beam and the vertical bracket form a triangle, the horizontal plate arranged on the longitudinal plate is obliquely arranged with the lower end close to the ground, and when bolts are inserted into pin holes on the upper part of the swing rod and the upper part of the vertical bracket of the frame, the swing rod can not swing relative to the vertical bracket of the frame, and the device can be used for exercising sit-ups; and when the bolts are drawn out from the pin holes on the upper part of the swing rod and the upper part of the vertical bracket of the frame, the swing rod can swing relative to the vertical bracket of the frame, and the elastic pull rope provides damping force for exercising the thigh strength, so the utility model has the advantages of simple structure and complete functions.