To test control effect of Fusarium oxysporum CS-20 against cucumber fusarium wilt in seedling stage,Fusarium oxysporum CS-20 and pathogenic bacteria were inoculated in cucumber seedlings successively,and its control effect was evaluated in terms of inoculation concentration and acting time.The results showed that when acting time and inoculation concentration were 11 d and 4×106 cfu/mL,the control effect of Fusarium oxysporum CS-20 against cucumber fusarium wilt was the best.