Unsymmetrical dimethylhydrazine is a high toxic substance, and the UDMH wastewater has always been an issue. A strain of bacteria was isolated to be used to degrade the UDMH wastewater. The strain of bacteria was screened from the activated sludge, that had been acclimated with the UDMH, and it could grow well in the medium with the UDMH as the only carbon and nitrogen source. It was identified to be Stenotrophomonas by the Biolog microbial identification system after the purification. Its logarithmic phase was from the 12th to the 18th hour in broth. The influencing factors include the temperature, the pH value, the initial UDMH concentration and the added different carbon sources, and their effects on the degradation were investigated. The results show that the optimal temperature and pH value for the strain growth were 30 to 35℃ and 7.2 to 8.0, respectively, and the optimal initial concentration of the UDMH was 50 to 80mg/L. And the addition of glucose could promote the degradation of the UDMH. Under the temperature of 35℃, the medium pH value of 7.2, the initial UDMH concentration of 80mg/L, and the inoculation of 1%, the highest degradation rate of the UDMH was 96.19% in 72h. When the initial UDMH concentration was changed to 120mg/L, the degradation rate of the UDMH was 71.87%, which shows that the strain of bacteria has a certain tolerance to the UDMH.