As an important noninvasive diagnostic tool, the positron emission tomography/computed tomography (PET/CT) plays a significant role in diagnosis and therapy of patients with diffuse large B-cell lymphoma (DLBCL). PET/CT, a standard imaging tool for initial accurate staging and response assessments, has replaced conventional CT in rituximab era. In this review, the definition, interpretation method, prognostic value and risk stratification of interim PET/CT are introduced to clarify the guiding significance of PET/CT in the diagnosis and theray of DLBCL, and the application of PET/CT scanning-guided prognostic factors and response-adapted therapy for DLBCL is summarized.