The process of the complete mixing method is the same as that of the traditional activated sludge method, and it is an improvement against the two disadvantages of the traditional activated sludge method. The difference is that the mixing tank is fully mixed and circulated in the aeration tank, and the returning sludge and inflowing sludge wastewater enter the aeration tank and are immediately fully mixed with the original mixed liquid. Its characteristics are: the water quality at each point in the aeration tank is basically the same, that is, the activated sludge concentration at the wastewater organic matter concentration is almost the same at each point. Therefore, the working conditions of the various parts of the pool are almost the same. In this way, the oxygen demand in all parts of the aeration tank in the complete mixing method is uniform, and there is no waste of oxygen; in addition, the complete mixing method is more suitable for changing the impact load. Has been homogenized.