Abstract: A method for identifying a bacterium in a biological sample, and a method for testing antibiotic susceptibility of a bacterium in a biological sample, comprising: step (1), centrifugally separating the bacterium from the biological sample; step (2), staining the bacterium obtained in step (1); step (3), fixing the stained bacterium in step (2) by electrostatic adsorption; step (4), injecting an extraction solution into a capillary tip, and then extracting metabolites of the single living bacterium by in-situ extraction; step (5), inserting an electrode into the capillary obtained in step (4), applying a voltage, and performing mass spectrometry. The method does not depend on incubation, and the identification and the antibiotic susceptibility testing of a bacterium in a biological sample of an early bacterial infection can be realized, and the method has the advantages of being rapid, having high sensitivity, capable of performing a non-targeting analysis, etc., and has good application prospects.