The invention discloses an annular spring washer and a vertical multistage pump thereof. The multistage pump comprises a bottom cylinder, a first-stage guide part, all stages of impellers, multiple middle guide parts, an outer cylinder, a final-stage guide part, an annular spring washer and a back cover, wherein the bottom cylinder and the back cover are mounted at the two ends of the outer cylinder; the first-stage guide part, the multiple middle guide parts and the final-stage guide part are mounted in the outer cylinder; all the stages of impellers are mounted in all the guide parts; the annular spring washer comprises four sections of axial positioning structures; the four sections of the axial positioning structures are connected in sequence to form an annular structure; each sectionof the axial positioning structure comprises a large arch pipe, a small arch pipe and a positioning horizontal pipe; the arc highest point of the large arch pipe in the annular spring washer is connected with the bottom of the final-stage guide part; and the positioning horizontal pipes are bonded and matched with a boss on the back cover. The annular spring washer cannot be permanently deformed after long-time use in axial fixation, so that the axial fixation reliability of a guide device of the vertical multistage pump is improved.