Abstract: Sequencing Batch Reactor（SBR）was used to enrich short-cut denitrifying phosphorus accumulating bacteria（SDPB）. The strain was isolated，purified and identified. Response surface methodology was applied to optimize the medium of bacteria. Results showed that Si was isolated and purified from SBR. Morphological/physiological/biochemical indicators and the phylogenic tree of 16S rDNA gene sequence measurements demonstrated that Si is similar to Acinetobacter beijerinckii. Biochemical properties also demonstrated that Si has the function of short denitrifying and phosphorus accumulating. Acinetobacter beijerinckii is a kind of SDPB. Through the analyses of response surface methodology，the order of key factors affecting the growth of Si is pH≈carbon source＞nitrogen source. The best medium of Si is carbon source of 4060mg/L，nitrogen source of 1090 mg/L with pH 8.0. The average turbidity of bacteria is 0.867.