[Objective] In order to alleviate the harm of cinnamic acid, an auto-toxic substance to the watermelon and other related crops, a bacterial strain with high efficacy of degradation of cinnamic acid was isolated from soils collected in watermelon field of Zhong-wei county, Ningxia. Its characteristics of cinnamic acid-degradation were evaluated. [Methods] A microbe which could effective use cinnamic acid was isolated. 16S rRNA gene sequence data was used to the strain identification. The degrading kinetics of cinnamic acid by strain R30 was determined by HPLC. A plant growth chamber test was performed to confirm the efficacy of R30 to resume the vitality of watermelon seedlings. [Results] A bacterial strain R30, which was isolated from watermelon continuous cropping soil, was identified as Exiguobacterium sp.. This strain could degrade 99% of cinnamic acid within 96 h at 30 °C, pH 7.0. Strain R30 was also found to degrade coumalic acid, ferulic acid, and benzoic acid efficiently as well as cinnamic acid. Plant growth chamber test indicated that strain R30 could efficiently alleviate the inhibition of cinnamic acid on watermelon seedlings. [Conclusion] The R30 strain possesses the ability of degrading a wide range of phenolic acids, thus has a potent applications in management of crop continuous cropping obstacles which caused by cinnamic acid, coumalic acid, ferulic acid, and benzoic acid.