The invention discloses a degradation bacterium for oil-base drilling cuttings, and a preparation method and an application method thereof, and belongs to the technical field of microbiological processing of oil-containing solid wastes. The degradation bacterium for oil-base drilling cuttings is composed of multiple microorganisms, and is prepared by performing fermentation culturing on three degradation single bacteria which are obtained by performing enriching, separation, purification and screening on bacteria in petroleum polluted soil. The degradation bacterium for oil-base drilling cuttings comprises pPseudomonas aeruginosa, kocuria kristinae and acinetobacter calcoaceticus, is used for degradation of petroleum composition in oil-base drilling cuttings, and has the substantial advantages of high oil removal efficiency and short processing period. When oil-base drilling cutting with the initial oil content less than 5% is processed by using the degradation bacterium for 5-30 d, the oil content can be reduced to 1% or less, and the oil removal rate can reach 80% or more. The degradation bacterium also has good application prospect when being applied to biological restoration of oil-containing soil and oil-containing sludge.