In order to determine the degradation of mixed bacterial suspension of five petroleum hydrocarbon degrading bacteria extracted in the laboratory on gasoline-contaminated soil, we had make use of gas chromatography-mass spectrometry to implement qualitative analysis on gasoline-contaminated soil compounds degraded by degrading bacteria in order to assess whether such mixed bacterial suspension has the ability to degrade the gasoline-contaminated soil. Moreover, Considering the factors of PH value, temperature, soil moisture content and inoculation amount of degrading bacteria, single factor test and multi-factor orthogonal test were adopted to determine the degradation rate with the purpose of optimizing the degradation conditions of gasoline-contaminated soil by the mixed bacterial suspension. The experiment has the following results. Firstly, under the condition of single factor test, it is found after comparing the organic components before and after the test, that these five degrading bacteria extracted in the laboratory have good degrading ability to the gasoline-contaminated soil. Secondly, from the relative peak area ratio chart, it is discovered that temperature and inoculation of degrading bacteria have more significant effects on the degradation of degrading bacteria than moisture content and pH. Thirdly, when the PH is between 6 and 8, the degradation temperature between 30℃ and 35℃, the moisture content between 15% and 25% and the inoculation amount of degrading bacteria between 1 ml and 2.5 ml, the degradation effect of mixed bacterial suspension is relatively obvious. Under the condition of multi-factor orthogonal test, the optimum degradation conditions of mixed bacterial suspension are as follows: temperature is 32℃, PH value is 7, inoculation amount of degrading bacteria is 1 ml and water content is 25%.