The invention belongs to the technical field of molecular biology, and discloses a pretreatment method for pathogenic-bacterium gene identification in clinical specimens. The pretreatment method includes the steps that incubation is carried out through a mixture of proteinase K, sodium dodecyl sulfate and potassium chloride, protein in cells and protein combined with DNA are digested, and the DNA is separated; then incubation is carried out through ammonium sulfate, sodium chloride and mannose, impurities are removed firstly, impurities are removed secondly with ethyl alcohol, and washing is carried out; the longest consumed time in the whole process is in 2.5 h, time is short, and DNA specimens with the high purity and the high concentration can be obtained when the thallus concentration is 10 CFU/ml.