Four psychrophilic bacteria are cultured in the laboratary to resolve the low domestic sewage treatment load at low temperature. Scanning electron microscope is used for observing the morphological feature and biological fluorescence spectroscopy is employed to measure the bioactibity of the four psychrophilic bacteria. The results show that the four bacteria are all from bacillus and have high bioactivity and strong adaptability. The bioactivities of psychrophilic bacteria are higher than those of mesophilic bacteria when the temprature is below 15 ℃. Therefore, it is necessary to add psychrophilic bacteria into domestic sewage to increase the degradation rates since the mesophilic bacteria almost lose their bioactivities when the temperature drops below 15 ℃. The value of the degradation rate is measured and the result shows that the removal ratio of tatal nitrogen increase 53.5% and the removal ratio of tatal phasphoras increases 80% in our experiment by using the mixed psychrophilic bacteria.