Abstract: The antagonistic substance of Pseudomonas aeruginosa can effectively antagonize Arthrinium phaeospermum (Corda)M.B.Elli. The yellow oily substances with strong microbe-inhibiting activity were included through silica gel column chromatography and UV elution after pretreatment of the filtrate of fermentation broth adopting trichloromethane extraction. By nuclear magnetic resonance and infrared spectrum detection, the compound was proved a phenazine pigment with aromatic rings, and with the chemical formula C₁₄H₁₀O₂N₂. Furthermore, the pigment stability test showed that illumination and temperature exerted slight effects on pigment activity. Light concentrate oxidizer and reducing agent exerted small effects on it, while the heavy concentrate was on contrary. The pigment activity was up to its max when pH was 7-8; when pH≤3, it was instability and almost with no bacteriostatic activity. Metallic ion could affect the pigment stability in varying degrees, Na⁺,K⁺,Ba²⁺,Ca²⁺ and Ag⁺ exerted a light effect on pigment's stability, however, Al³⁺,Cu²⁺,Fe³⁺,Pb²⁺ exerted a heavy influence, which nearly caused it lost all activities.