The invention provides a Pseudomonadaceae petroleum degrading bacterium L-1, a microbial mixed agent of the Pseudomonadaceae petroleum degrading bacterium L-1 and an in-situ remediation method of petroleum-contaminated soil. The preservation number of the Pseudomonadaceae petroleum degrading bacterium is CGMCC NO.16557. The microbial mixed agent contains the Pseudomonadaceae petroleum degrading bacteria in the preservation number being CGMCC NO.16557 and indigenous bacteria. By the aid of the method, the content of petroleum hydrocarbon and polycyclic aromatic hydrocarbon in petroleum-containing sludge can be reduced effectively, harmless treatment of the petroleum-containing sludge can be realized, harms caused by the contaminated soil to human bodies can be eliminated, and ecological functions of the soil can be restored. Thus, degradation of the petroleum hydrocarbon is used as a starting point, microbes having the obvious degrading effect on soil petroleum are separated and cultivated, and the specific implementation measure of an on-site petroleum-contaminated soil microbial in-situ remediation technology is further provided. The petroleum-contaminated soil with the concentration being 3% can be degraded by 77% after 30 days.