The invention discloses a two-stage downward opening type weir gate. The two-stage downward opening type weir gate comprises a weir frame, wherein a lower weir plate structure is arranged in the weir frame, a cavity is formed in the lower weir plate structure, an upper weir plate is arranged in the cavity, an upper weir plate stop block is arranged at the top of the cavity, and a driving structure is connected onto the upper weir plate; first sealing structures are arranged between the upper weir plate and the lower weir plate structure, and second sealing structures are arranged between the lower weir plate structure and the weir frame; each first sealing structure comprises a first bottom ring fixed on the cavity, a first seal ring in seal fit with the upper weir plate is embedded in the first bottom ring, a first inner hole is formed in the first seal ring, and a first batten is inserted in the first inner hole and fixedly connected with the first bottom ring; each second sealing structure comprises a second bottom ring fixed on the weir frame, a second seal ring in seal fit with the lower weir plate is embedded in the second bottom ring, a second inner hole is formed in the second seal ring, and a second batten is inserted in the second inner hole and fixedly connected with the second bottom ring. The two-stage downward opening type weir gate not only saves underground excavation space, but also is reliable in sealing.