Abstract: A heterotrophic nitrification-aerobic denitrification bacterium named X12 was isolated from the filter mouth of Dongping shrimp pond，Gram negative bacteria，bacillus.The characteristics of denitrification of X12 was studied under different conditions and the optimal conditions for its growth and denitrification were followed as carbon source was sodium citrate，30 ℃，160 r/min，pH 7.0.Increasing of nitrogen concentration in the medium and immobilization technology were to be studied in the subsequent step.This strain showed great potential in biological nitrogen removal of wastewater with high salt from mariculture and industries.