A water flow energy converting device comprises an upper end cover, a lower end cover, an arc-shaped volute connecting the lower end cover and the upper end cover and a volute front retaining plate. A shaft hole is formed in each of the upper end cover and the lower end cover. A water wheel shaft is mounted in the shaft holes. A blade disc is fixedly connected to the middle of the water wheel shaft. Blade rods are connected to the upper portion and the lower portion of the blade disc. Blades which can rotate around the blade rods are movably connected to the blade rods. The volute is provided with a water inlet and a water outlet. Water stopping plates for stopping water passing are disposed between water inlet and the water outlet. The water stopping plates are disposed on the volute front retaining plate, the upper end cover or the lower end cover. Intervals allowing the blades, the blade rods and the blade disc to pass are formed between the water stopping plates or between the water stopping plate and the upper end cover and the lower end cover. Water flow pushes the water wheel shaft to rotate from the water inlet to the water outlet. The water flow energy converting device is simple in structure, low in manufacturing cost and capable of sufficiently utilizing natural water flow energy, and the water flow is efficiently utilized for power generation.