Objective To study the risk factors,methods of etiologic diagnosis and treatment of disunion of fracture due to delayed infection after the internal fixation. Methods The clinical data including bacterial tests, clinical manifestation and the administration of antibiotics , of 24 cases of disunion of fracture due to delayed infec-tion after the internal fixation were retrospectively analyzed. Results 22 strains of pathogenic bacteria were distin-guished with a detection rate of 91.67% in the 24 cases. 16 strains of these bacteria were gram-positive,and 6 gram-negative. The gram-positive ones were all sensitive to vancomycin and teicoplanin. The gram-negative ones were all sensitive to imipenem and meropenem. It was common for patients to take antibiotic after operation. Conclusion More infection is caused by gram-positive bacteria than by gram-negative ones. Antibiotic therapy based on the bacte-rial test is reasonable and necessary besides surgeries.