The invention relates to the field of biotechnology and environmental protection, in particular to a microbial inoculant, and particularly relates to a complex microbial inoculant for petroleum hydrocarbon and benzene series treatment as well as a preparation method and application thereof. The active ingredients of the complex microbial inoculant comprise aspergillus oryzae, streptomyces, pseudomonas putida, pseudomonas alcaligenes, brevibacterium epidermidis and Erwinia; and the complex microbial inoculant is especially suitable for treating soil polluted by petroleum hydrocarbon and benzeneseries. After the complex microbial inoculant disclosed by the invention is added into the soil polluted by the petroleum hydrocarbon and benzene series, indigenous degrading flora can be rapidly propagated, and the remediation process can be rapidly started; in the repairing process, the indigenous degrading bacteria are always in the dominant flora status, and high degradation efficiency is kept for a long time through the synergistic cooperation of the flora in the complex microbial inoculant; and finally, the polluted soil is completely repaired, the degradation rate of petroleum hydrocarbon and benzene series is high, and the removal rate of BTEX and TPH can reach 98% or above.