Abstract: The oxygen increasing mechanism of rotary cylindric aerator is analysed in this paper. The main factors that affect oxygen increasing efficiency of this aerator are found out through laboratory experiments, and the optimal combination of these factors is also obtained by analyses and experiments. To increase the speed of the rotary cylinder can increase the quantity of the air entering the water,decrease the diameter of the air bubble, and increase the turbulence and convective circulation of the water, which can increase the oxygen increasing efficiency. The conclusions above provide the basic foundations for the design of rotary cylindric aerator.