Abstract: The trial is mainly about factors (such as temperature, illumination and so on) which affected colonizing of Trichoderma on leaf surface. The results showed that temperature and illumination were major factors which affected colonizing of Trichoderma on leaf surface. The maximum temperature rang was 25~30℃ for Trichoderma colonization on tomato leaf surface. Continuous illumination was benefit to colonization of Trichoderma on leaf surface, however no much affection of humidity was found on the Trichoderma colonization. There was little affection of chemical fungicide 75% mancozeb on colonizing ability of Trichoderma when the fungicide was sprayed on the leaf surface as compared with other fungicides. It was available to weaken the exclusion of orginal microflora to biocontrol agent, and then improve the biocontrol efficiency of Trichoderma sp against grey mold on leaf surface by adjusting the concentration of applied fungicide on the leaf surface.