Abstract: Bacillus subtilis strain TL2 was studied, which was proved to be colonize inside of tea plant and had good effect of preventing tea leave spot diseases. The fermentation conditions, processing technique, accessory ingredient and control effect against leave spot diseases in field of this strain were tested. The result indicated that its optimum conditions of producing antimicrobial protein should be nitrogen source (peptone), cultivation temperature (35℃), carbon source (sucrose), cultivation time (72h), original pH (6.6) and liquid medium volume (50ml/250ml). Its optimum conditions of solid state fermentation was tested to be nitrogen source (defatted soybean), carbon source (bran), moisture content (25ml/250ml), inoculum concentration (4%), cultivation temperature (35℃) and original pH (6.6). Four kinds of accessory ingredient (calcium carbonate, kaoline, talcum powder and kieselguhr), one kind of wetting dispersants (calcium lignosulphonate) and two kinds of protective agent from UV (humic acid and dextrine), were screened. The microbial inoculum (wettable powder) was tested to have good effect of preventing tea leave spot diseases (70%) in tea garden, which was appropriate to the effect of Sanmate as a control.