Based on the situation of the water pollution and the destruction of the Qionghai lake, the author advances three projects of treating sewage around the Qionghai lake -- the aeration, the biological rotating disc and the bio-contact oxidation. With a detailed and thorough analysis of the application, the technology and the economy, the author selects the bio-contact oxidation to be the best one. This is a positive guide to the construction of the ecological environment of the Qionghai lake.