The invention discloses a method for rapidly detecting gram negative and positive bacteria. The method comprises the following steps: coupling nano magnetic beads to a lipoteichoic acid antibody or an aptamer, and sealing uncoupled sites, so as to obtain positive bacteria-enriched magnetic beads; coupling the nano magnetic beads to a lipopolysaccharide antibody or the aptamer, and sealing the uncoupled sites, so as to obtain negative bacteria-enriched magnetic beads; and respectively mixing the positive bacteria-enriched magnetic beads or the negative bacteria-enriched magnetic beads with a detection sample evenly, incubating, washing, adding a fluorescent labeling second antibody or an enzyme labeling second antibody, washing and determining the result. Through the manner, according to the method for rapidly detecting gram negative and positive bacteria, the low-concentration bacteria polluted sample can be detected; the operation time is shortened; automation is easy to achieve; the operation is simplified; the detection accuracy is ensured; quantitative determination can be achieved; the method can be widely applied to screening of bacterial pollution in the fields of medical health, food, medicines and the like; the problems of presence and absence of bacteria, the bacteria content and the like are solved; and the rapid, accurate and reliable detection requirements can be met.