The invention discloses a vertical-type air-flotation device, and relates to improvement on the structure of the vertical-type air-flotation device. The vertical-type air-flotation device comprises a tank body, a dissolved air releasing system and a steady flow cylinder, wherein the steady flow cylinder is arranged in the tank body; a sewage inlet pipe is arranged at the top of the tank body; a water outlet pipe is arranged on a tank wall of the middle-lower part of the tank body; the dissolved air releasing system is arranged at the bottom of the steady flow cylinder; the water inlet pipe stretches into the steady flow cylinder and corresponds to the dissolved air releasing system; the steady flow cylinder is provided with bell-mouthed upper and lower openings; and the water inlet pipe is provided with a bell-mouthed outlet. The vertical-type air-flotation device has three bell mouths, during working, water flowing from the bell-mouthed outlet of the water inlet pipe diffuses in the big bell-mouthed lower opening of the steady flow cylinder; a dissolved air releasing device ejects high-pressure air flow towards the sewage which flows and diffuses from top to bottom so as to enable the sewage to form air bubble and fast diffuse to the lower bell-mouthed opening; emulsified oil, oil particles, floccule and bigger impurities in the sewage are attached to the surface of the air bubble; and then the emulsified oil, oil particles, floccule and bigger impurities float upwards in the steady flow cylinder to the upper bell-mouthed opening of the steady flow cylinder to be removed by a skimming device.