NOVELTY - Preparation of bioactive substance containing vetiver extract, involves extracting vetiver leaves with alcohol to obtain alcohol crude extract, dissolving alcohol crude extract in 70% ethanol aqueous solution, then extracting with petroleum ether, filtering petroleum ether layer and concentrating to obtain vetiver petroleum ether extract, removing ethanol from residual liquid by concentrating and fixing constant with water to original volume to obtain residual liquid (I), and extracting residual liquid (I) with ethyl acetate to obtain vetiver ethyl acetate extract.    USE - The vetiver extract is useful for preventing and controlling plant pathogenic fungal infection, where the vetiver petroleum ether extract and vetiver ethyl acetate extract exhibit antimicrobial activity on Rhizoctonia solani, Colletotrichum musae, microorganism causing anthracnose of grape, R.solani infecting cucumber, Fusarium oxysporum infecting cucumber, and Alternaria solani that causes tomato early blight.    ADVANTAGE - The vetiver extract exhibits low toxicity and does not cause environmental pollution. The fungus does not develop resistance with respect to vetiver extract.    DETAILED DESCRIPTION - Preparation of biological active substance containing vetiver extract, involves (a) placing leaves of vetiver in shade to dry until the moisture content is less than 5%, and then cutting into 1-2 cm, (b) immersing the pre-processed raw materials in industrial alcohol based on weight ratio of 1:25-40 at room temperature, immersing for 3-8 days every time, filtering and mixing the extracts, decompressing and concentrating the extract in water bath of 45-55 degrees C to obtain pasty alcohol crude extract, (c) dissolving the alcohol crude extract in 70% ethanol aqueous solution based on ratio of weight to volume of 1 kg:2-6 L, then adding petroleum ether, stirring, extracting for three times for 4 hours every time, layering, filtering petroleum ether layer, decompressing and concentrating in water bath of 35-48 degrees C to obtain black pasty substance (vetiver petroleum ether extract), removing 70% ethanol from the residual liquid by decompressing and concentrating, and fixing the constant with water to the original volume to obtain residual liquid (I), and (d) extracting the residual liquid (I) with equal volume of ethyl acetate for three times and 4 hours every time, filtering, decompressing and concentrating the ethyl acetate layer in water bath of 40-50 degrees C to obtain vetiver ethyl acetate extract.