[Objective] To reveal the relationship between the main influencing factors and the level (orthogonal design) of microbial in situ remediation in order to provide a theoretical basis for the parameter design of bio-remediation engineering in oil-contaminated sites.[Methods] The effects of pollution intensity, nutrition, oxidant, surface active agent and inoculation amount on soil remediation were investigated by orthogonal design with 5 factors and 4 levels in the experiment.[Results] After the preliminary screening of crude oil as the sole carbon source, 16 dominant bacteria strains for petroleum hydrocarbon degradation were obtained. By the bacterial rescreening, two symbiotic fungi DPF₂ and DPF₄ were obtained. The highest synergistic degradation rate was 87.77% after 7 days. The degradation rate of oil-contaminated soil was the highest when the oil pollution intensity was 10 after 60 days, and the degradation rate of oil-contaminated soil reached to 94.12%. The degradation rate of oil-contaminated soil with pollution intensity of 25 was 90.17%. SPSS data analysis showed that oxidants, surfactant and nutrients were the most important factors affecting bio-remediation, followed by the intensity of contamination and the number of bacteria.[Conclusion] The initial addition of surfactant, oxidants, and nutrients could be of great significance to petroleum bio-remediation. The pollution intensity had a certain effect before 35 days, and had the least influence in the later stage of remediation. During the whole remediation process, the mean variance of inoculation amount was the smallest compared with other factors, so the factor level had no significant effect on the oil degradation ability.