The invention relates to a method for modifying magnetic bentonite by a biosurfactant. The method comprises the steps of firstly burying straws and rice husks in farmland soil for composting, performing enrichment culture on compost and domesticating a biosurfactant to generate a bacterial strain, continuously performing fermental cultivation, re-suspending fermentation liquor by using dichloromethane, filtering, extracting, centrifuging, and collecting sediment, thus obtaining a purified biosurfactant. The purified biosurfactant is used for replacing a conventional chemical surfactant, modifying the magnetic bentonite, and preparing to obtain a novel adsorber; the novel adsorber is applied to removal of uranium in low-concentration uranium-containing wastewater. The adsorber has good adsorptive property, needs main raw materials of agricultural waste biomass and natural minerals, is pollution-free to environment, and truly realizes resource conservation and environment friendliness. The method is simple, mild in reaction condition, and easy in magnetism control, and the uranium content in the low-concentration uranium-containing wastewater with the concentration of 0.45-0.55 mg/L can be reduced by 95 percent or more.