The invention relates to a method for preparing a bacillus subtilis lipopeptid biosurfactant, which is characterized in that the adopted bacterial strain is efficient lipopeptid producing strain bacillus subtilis BIT09S1,BIT09S2 and BIT09A2, and the lipopeptid biosurfactant is prepared by taking cheap molasses, pulse flour, konjac gum finemeal, guar gum and gum breaking liquid of modified guar gum as carbon sources for the culture medium; adding other nitrogen sources, phosphorus sources, inorganic salt components and nutrient elements into the culture medium; and carrying out fermentation, separation and purification. The raw materials used for producing lipopeptid by the method are easily obtained and can be enormously purchased. The crude extract of the obtained lipopeptid biosurfactant Surfactin can be used in various drilling and production processes such as oil-gas field fracturing, acidizing, de-plugging, controlling and water shut-off, oily water treatment, environment renovation and the like, and the biosurfactant has wide prospect.