The invention relates to a phenolic acid type allelochemical degrading bacterium and the preparation and the application of a microbial inoculum thereof. The BJS-1-3 bacterial strain disclosed by the invention is from rhizosphere soil of perennial poplars in Tai'an City, Shandong Province, China, and the soil is artificially gathered, screened and purified to obtain the bacterial strain. The bacterial strain has a high degrading capacity to benzoic acid, and phenolic acid type allelochemicals, such as ferulic acid, p-hydroxybenzoic acid, vanillin, cinnamic acid and phloridzin, can be respectively used as a unique carbon source in which the bacterial strain grows and propagates, and the bacterial strain can stably propagate in the rhizosphere of poplars, apple trees and cucumber plants. Through the adoption of the microbial inoculum prepared from the bacterial strain, the succession cropping obstacles of plants, such as the poplars, the apple trees and the cucumber plants, due to the accumulation of phenolic acid type allelochemicals can be effectively prevented and treated. The preparation technology of the microbial inoculum is simple, the fermentation period is short, the cost is low, and the industrialized production is facilitated.