To explore the Symbiotic and Epiphyte bacterium DNC₂ from Strongylocentrotus intermedius, the morphological, biochemical and physiological characteristics of the strain were researched and the 16S rDNA sequences of it were analyzed. The univariate experiment and orthogonal test of L₁₆(4⁵) were carried out to optimize the fermentation conditions for antibacterial activity. Symbiotic and Epiphyte bacterium DNC₂ was identified as Bacillus subtilis. The optimal fermentation conditions were obtained as fermentation at 35 ℃ for 120 h with initial pH 9, and the optimum fermentation medium was determined as beef extract 0.3% and peptone 0.6%. The optimized fermentation broth also showed good effect on inhibiting the growth of 8 kinds of fungus. The inhibition rate was 92% against Trichothecium roseum (Bull.) Link, 89% against Botrytis cinerea Pers and A.solani (Ell&Mart).sorauer, 88% against Ralstonia solanacearum, 81% against Mucor mucedo (L.)Brefeld, 73% against Fusarium oxysporum f.sp.niveum, 72% against Fusarium oxysporum of Cotton and 52% against Fusarium moniliformis.