Recently, with the growth of living standards and income, the interest to the environment pollution is increased. According to the reinforcement of a water pollution regulation, a study for an efficiency improvement of sewage disposal carried out. There are many ways to efficiency improvement of sewage disposal. One of them way is to increase the dissolved oxygen content of water in water treatment tank. In this paper, we suggest a nozzle which can generate micro bubbles and increase the dissolved oxygen content of water. The micro bubbles through the flow of spiral and crash is generated in nozzle. This results of analysis show bad result that is large size of bubble by flow of crash because of limited velocity to inlet condition. The bubble size of 20~50 ㎛ has captured about 78% of the air to the nozzle using the flow of spiral in control volume. We can most likely increase efficiency improvement of sewage disposal by this study.