From habitat soil of Amanita phalloides, isolation and screening of bacteria strains against the Phytophthora parasitica var. nicotianae were conducted and pot experiment was used to investigate the control effect of the antagonistic bacteria strain against tobacco black shank. The findings demonstrated that, strain DE4-5 showed wide anti-fungi activity, and the inhibition rate of strain DE4-5 on Phytophthora parasitica var. nicotianae reached 78.22%. Based on morphological and biochemical characteristics, strain DE4-5 was initially determined to be Pseudomonas. Combined with the analysis of conserved sequence of 16S rDNA and the sequence of the auxiliary gyrA gene, strain DE4-5 was systematically assigned to the Pseudomonas flax genus and given the name Pseudomonas lini DE4-5. Bioactivity assay showed that strain DE4-5 could degenerate phosphorus and potassium. By resolving phosphorus and potassium, strain DE4-5 was able to produce IAA, protease, cellulase, and urease. Pot experiment showed that the incidence of tobacco black shank in prevention and treatment groups with strain DE4-5 were 24.79% and 39.24%, respectively; the disease index of tobacco black shank in prevention and treatment groups with strain DE4-5 were 26.31% and 29.37%, respectively; and the control effect in prevention group and treatment group reached 69.14% and 63.98%, respectively.