A vertical self-priming pump includes a pump body (10), a motor (20) and a medium reflux blocking device (30). A middle division board (11) is provided in the pump body (10). A flow guide body (40) is fixed on the middle division board (11). The motor (20) is fixed on the pump body (10) for driving a pump shaft (21) rotating. An impeller (22) is fixed on the lower end of the pump shaft (21). A reflux gap passage (24) is formed in the clearance between the outer circumferential surface of the impeller (22) and the internal wall of the flow guide body (40). The medium reflux blocking device (30) includes a rotating ring (31) and a fixed ring (32) oppositely arranged at upper and lower positions, and an elastic supporting sleeve (33). The rotating ring (31) is embedded in the upper surface of the impeller. The elastic supporting sleeve (33) is fixedly mounted on the upper surface of the flow guide body. The fixed ring (32) is embedded in the lower surface of the elastic supporting sleeve. The medium reflux blocking device reduces the volume loss caused by the reflux and improves the efficiency of the vertical self-priming pump.
