Abstract: This study focused on the screening of highly efficient petroleum degrading bacteria. The petroleum-degrading strain X10 is based on diesel as the sole carbon source, which was separated by primary and secondary screening from the petroleum-contaminated coastal area of Hainan Province. 16S rDNA sequencing was showed that the strain was identified as Achromatium. Diesel was degraded is 69.39%. Meanwhile, the effects of pH, culture temperature, initial inoculation amount and external carbon source on the degradation ability of diesel were studied. The results showed that strain X10 had the best degradation effect at the initial pH 6.0 under the experimental conditions. The strain can adapt to a wide range of PH value. The culture temperature had a significant influence on the petroleum degradation rate. The degradation rate was 67.94% at 30℃, which is the optimum temperature. The optimum inoculation amount was 5%. The degradation rate of diesel was enhanced by the addition of external carbon sources, such as glucose, lactose and mannitol. However, there were no significant differences among these external carbon sources.