The water purification ability of one strain of photosynthetic bacteria（PSB），which was isolated from fish pond sediment，to domestic sewage and fish pond water was analyzed in this paper. The results show that this strain of PSB had good water purification abilities in that nitrites，ammonical nitrogen and chemical oxygen demand of domestic sewage were reduced by 66.7%、66.6% and 54.2% after treated with this strain of PSB，and those of fish pond water were reduce by 57.3% 、74.8% and 46.1% respectively. This strain of PSB had a very good water purification effect.