The screening of isolates and the assay of biocontrol mechanisms of Trichoderma were studied systematically in laboratory and greenhouse in vivo. The proteins tolerant to benzimidazole in Trichoderma strains were purified, and their physical and chemical properties were detected. Compared their biological activities in vitro and vivo in greenhouse, nine biocontrol strains (including Ty-10-2,LTR-2,Tj-5-1,Tj-5-4,Ty-11-1,Tj-11-3,Ty-11-3,Tj-3-3-2,Tj-3-3-4) were screened. These biocontrol strains had faster rates of growth and higher inhibition to gray mould (Bortrytis cinerea), and the inhibition was stable. The effects of controlling gray mould in greenhouse with the screened Trichoderma strains were 70% and 50% in vivo. Induced by the substrates including benzimidazole, UV rays and nitrosoguanidine, four strains were screened. They were Ty-10-2,LTR-2,Tj-5-4,Ty-11-3. After being cultured for 24 h, conidiospores of tolerant strains germinated but the sensitive ones didn’t. Compared with the hyphae of the tolerant strains, the sensitive hyphae, front became thinner and shorter. Experiments of biocontrol mechanisms showed as followed: some genes had mutated, transcripted at different levels and translated into some tolerant proteins, while some genes had opposite changes. In the whole, the soluble proteins in cells had increased in quantity. The esterase isoenzymes in the tolerant strains decreased at different levels. After being induced, some genes mutated and some genes, transcription decreased and even diminished. None were screened from UV rays and nitrosoguanidine. The screening of isolates and the assay of biocontrol mechanisms of Trichoderma were studied systematically in laboratory and greenhouse in vivo. The proteins tolerant to benzimidazole in Trichoderma strains were purified, and their physical and chemical properties were detected. Compared their biological activities in vitro and vivo in greenhouse, nine biocontrol strains (including Ty-10-2, LTR-2, Tj-5-1, Tj- 5-4, Ty- 11-1, Tj- 11-3, Ty- 11-3, Tj- These biocontrol strains had had faster rates of growth and higher inhibition to gray mold (Bortrytis cinerea), and the inhibition was stable. The effects of controlling gray mold in greenhouse With screened Trichoderma strains were 70% and 50% in vivo. Induced by the substrates including benzimidazole, UV rays and nitrosoguanidine, four were screened. They were Ty-10-2, LTR-2, Tj-5-4, Ty -11-3. After being cultured for 24 h, conidiospores of tolerant germinated but the sensitive ones did not. Co mpared with the hyphae of the tolerant strains, the sensitive hyphae, front sensitive thinhair, the sensitive hyphae, front turned thinner and shorter. Experiments of biocontrol mechanisms showed as followed: some genes had mutated, transcripted at different levels and translated into some tolerant proteins, while some genes had opposite changes. After the induced, some genes mutated and some genes, transcription decreased and even diminished. None were screened from UV rays and nitrosoguanidine.