Abstract: In order to obtain one stable and more effective antagonist, Strain Y1-3 screened by our lab was selected to be an initial strain. One mutant strain UY5-22 which appeared the best inhibition effect against green mold on citrus fruits was obtained, by ultraviolet irradiation for 30 s. The strain UY5-22 grew faster than the initial strain Y1-3, and OD value of its diluted suspension was high up to 0.440 when cultivated for 14 h. In the experiment of acupuncture inoculation on citrus fruits in vivo, the incidence of green mold was reduced by 82.40% and 21.38% respectively compared with CK and initial strain. All tested antagonistic index of mutant strain UY5-22 was the highest.