The invention provides a spiral-blade opposite-rotation type double-runner water turbine. The water turbine comprises a diffusion section, a square-circle transition section connected with the diffusion section, a shell connected with the square-circle transition section, and a tail water section connected with the shell, and further comprises a front-section runner and a rear-section runner whichare arranged in the shell; and each of the front-section runner and the rear-section runner comprises an inner cylinder, a spiral blade with a double-helix structure arranged on the inner cylinder and an outer cylinder arranged outside the spiral blade, the inner cylinders, the spiral blades and the outer cylinders are in an integrated structures correspondingly and rotate around a fixed shaft arranged in the shell, and the rotating directions of the front-section runner and the rear-section runner are opposite. According to the water turbine, the two-section structure design is adopted, so that a long flow channel can reduce the pressure gradient in the flow channel; the front-section runner and the rear-section runner rotate reversely, so that a rotating flow state can be eliminated; and the inner cylinders, the spiral blades and the outer cylinders integrated structures prevent cavitation between the blades and the outer cylinders correspondingly, so that the probability of mechanical damage of fishes is reduced.