Abstract: Classical physiological and biochemical methods, Biolog, and 16SrDNAanalysis were used to identify the strain X3 which could control cucumber seedling damping-off.Physiological and biochemical identification showed that it belonged to Pseudomonas aeruginosa, but Biolog identification showed it was P.spinosa.16SrDNA determination and analysis was used for further identification, which showed that the 16SrDNA sequence of X3 shared 93.7% homologies with published sequence of P.aeruginosa from GenBank, and both sequences constituted a branch in Phylogenetic tree.Based on these results, it is considered that the strain X3 belongs to one strain of P.aeruginosa.