We report the case of a 48-year-old male who presented with right lower abdominal pain and a mass for 2 weeks and got constipation for 5 days. An abdominal CT scan conducted before admission at other hospitals revealed an obstruction in the blind ascending colon, which was suspected to be a malignant tumor. Proctoscopy revealed peritoneal implantation metastasis and multiple pelvic lymph nodes. Physical examination was unremarkable except for multiple lymph node enlargements in the inguinal area, without pain. A whole-body contrast-enhanced FDG-PET/CT revealed lymphoma involvement in the ascending colon, peritoneum, bone marrow, and lymph nodes in multiple regions of the body, with DLBCL as a suspected diagnosis. Pathological findings from the colonoscopy revealed atypical lymphocyte infiltration and Immunostaining indicated the presence of atypical lymphocytes with Ki-67 (90%) and tested positive for CD20, CD19, CD10, and BCL-6. Based on the above findings, stage IV DLBCL was diagnosed. Furthermore, EBV-DNA amplification was positive. The patient received R-CHOP treatment for 2 days before experiencing symptoms of fevers, chills, and abdominal pain. He underwent emergency surgery due to intestinal perforation, and preoperative blood tests revealed HIV-positive. The prognosis for the patient is poor due to sepsis.