In the previous study,a biological control strain Bacillus subtilis BS5 with a strong antagonism effect against several phytopathogens was isolated. A low temperature biocontrol strain named BS303 was obtained by inducing strain BS5 with UV. The activity of biological control of BS303 was investigated with plate confrontation essay and greenhouse plant pot. Results showed that the antagonism activity of BS303 against four pathogenic fungi at 20℃ was stronger than that of BS5. The protect index of BS303 and BS5 against Fusarium oxysporum f. sp. melonis at 28℃ was 0.701,and 0.667, with no significant difference between them. However,the protect index of BS303 (0.767) against Fusarium oxysporum f. sp. melonis at 20 ℃ was higher than that of BS5 (0.557).Spread plate and RT-PCR were used to determine the colonization dynamics of biological control bacteria and phytopathogen fungi in soil. The results showed that both biological control strains fitted and established well in soil. The colonization dynamics of BS303 strain was better than that of BS5 (wild type). Number of the phytopathogen fungi was significantly decreased when the biological control bacteria were applied.