Abstract: Abstract: Algae has been studied for many years about its characteristics of rapid breed, easily obtained, high adsorption capacity and low nutrition demands and so on. The emission of aquaculture wastewater will caused severe damage on environment. Therefore, how to remove the compound of nitrogen and phosphorus from aquaculture wastewater becomes a serious problem around the world. Based above, many researchers have been focusing on this field and a lot of achievements have been found. Many environmental factors could influence on the growth of algae, including temperature, illumination and nutrition. For heterotrophism, carbon, nitrogen and phosphorus are the three most important factors influencing on the growth of Chlorella pyrenoides. Microalgae consist of several varieties, including Cyanophyta, Chlorophyta, Chrysophyta and Rhodophyta. Chlorella pyrenoides is belonged to Chlorophyta. Until now, studies of Chlorella pyrenoides have mainly focused on the processing, especially in the field of producing biodiesel, but few studies focused on the wastewater treatment by Chlorella pyrenoides. This study carried out the following experiments: the enrichment, isolation, purification and nutritional ingredient analysis for Chlorella pyrenoides. Then, the effect of treating with wastewater by Chlorella pyrenoides was carried out, including the removal of total nitrogen, total phosphorus and reducing COD. Chlorella pyrenoides was isolated from aquaculture wastewater with BG-11medium. The morphology and components of Chlorella pyrenoides were observed by phase contrast microscope and Fourier transform infrared spectrometer (FT-IR), respectively. The crystal structure of Chlorella pyrenoides was determined with X-ray. Protein and fat contents were measured by Kjeldahl determination and organic solvent extract method, respectively. The effect of treating with wastewater by Chlorella pyrenoides was tested with national standard methods. Chlorophyll a was extracted and analyzed with acetone extract method. The morphology observation with phase contrast microscope showed that Chlorella was belonged to Chlorella pyrenoides. FT-IR analysis showed that two peaks appeared at the wave numbers of 1 080 and 1 240 cm-1, which proved high contents of protein, carbohydrate and fat contained in Chlorella pyrenoides. X-ray diffraction spectrogram showed two main peaks appeared at about 32° and 20°, which proved both protein and fat were contained in Chlorella pyrenoides. Quantitative analysis indicated that contents of protein and fat were 45.6% and 8.1%, respectively. Correlational study indicated that the negative correlation of the increase of Chlorophyll a in Chlorella pyrenoides with the decrease of total nitrogen (T-N) and total phosphorus (T-P) remained in the wastewater. The removals of COD, total nitrogen (T-N) and total phosphorus (T-P) by Chlorella pyrenoides were 70.9%, 23% and 34.7%, respectively. Based on above results, the capability of treating with wastewater by Chlorella pyrenoides was proved in this study. Therefore, this study could provide a reference for the exploitation of a new bioresource and the water environment treatment.