The invention relates to the field of micro-alga biotechnologies, in particular to a symbiotic bacterium system for increasing biomasses of scenedesmus obliquus and improving the quality of grease and the stability of culture systems and application of the symbiotic bacterium system. The symbiotic bacterium system comprises the scenedesmus obliquus and symbiotic bacteria. The symbiotic bacteria include one type or a plurality of types of brevunmdimonas sp., rhizobium sp., pseudomonas sp. and acidovorax sp. The symbiotic bacterium system and the application have the advantages that the symbiotic bacteria and mixed floras of the symbiotic bacteria are applied to scenedesmus obliquus culture procedures, extracellular substances and oxygen which are generated by the scenedesmus obliquus can be consumed by each single type of symbiotic bacteria and the mixed floras, carbon dioxides can be generated to be utilized by the scenedesmus obliquus, micro-environments favorable for growth of the scenedesmus obliquus can be created, and accordingly substance exchange and metabolism of the scenedesmus obliquus, the symbiotic bacteria and the mixed floras can be promoted.