The invention discloses a single-tank double-stage rotational-flow air flotation device with an adjustable flow stabilization cylinder. The single-tank double-stage rotational-flow air flotation device comprises an oval upper sealing head, a tank body and an oval lower sealing head which are successively connected with each other, wherein a primary oil outlet is formed in the oval upper sealing head; a tangential inlet is formed in the upper part of the tank body; a secondary oil outlet is formed in the lower part of the tank body; the flow stabilization cylinder with adjustable height is arranged in the tank body and comprises a horn-shaped outer sleeve; the horn-shaped outer sleeve is fixedly connected with the inner wall of the tank body and is provided with opened top and bottom; an inner sleeve moving along an axial direction is embedded in the lower part of the outer sleeve; the bottom of the inner sleeve is fixedly connected with a horn-shaped cylinder; the periphery of the lower part of the horn-shaped cylinder is in sealing contact with the inner wall of the tank body and is used for dividing the inside of the tank body into an upper primary separation area and a lower secondary separation area; a flow guide groove is formed at the periphery of the horn-shaped cylinder; the inner sleeve is communicated with the horn-shaped cylinder; an oil discharging pipe is arranged in the inner sleeve along the axial direction and is communicated with a secondary oil outlet. The single-tank double-stage rotational-flow air flotation device is capable of adjusting the space ratio of the upper primary separation area and the lower secondary separation area by using the adjustable flow stabilization cylinder, and is adaptable to wider flow fluctuation.