Objective To explore the application of positron emission tomographycomputed tomography (PET-CT) in the diagnosis and treatment of diffuse large B-cell lymphoma (DLBCL). Methods The clinical data of 86 DLBCL patients were analyzed retrospectively. All patients were given PET-CT examination before and after treatment, and the diagnostic value of PET-CT in the DLBCL staging and the PET-CT imaging features were analyzed. According to the treatment effect, the patients were divided into complete remission group (CR group, n=35), partial remission group (PR group, n=33), disease stabilization group (SD group, n=8) and progression group (PD group, n=10). The maximum change rate of standardized uptake value (ΔSUVmax) and the lesion diameter were compared before and after treatment among four groups. Results The diagnostic accuracy of PET-CT for DLBCL staging was 91.9% (79/86). The PET-CT imaging features were changed in different degrees before and after treatment, and there were significant differences in the ΔSUVmax among four groups (P<0.05). There was no significant difference in lesion diameter among four groups (P>0.05). Conclusion PETCT can provide reliable imaging basis in the diagnosis and treatment of DLBCL, and has high clinical value.