A patient, male, 57 years old, was recently admitted. Physical examination revealed a huge occupying pelvic lesion, no difficulty in urination, no hematuria; no difficulty in defecation; pelvic MRI findings: bladder filling was possible, no significant thickening of the bladder wall was seen; a huge lobulated soft tissue tumor, about 10.2×5.9 cm, was seen between the prostate and the left seminal vesicle area and rectum, and the tumor was compressed with the rectum and the right seminal vesicle gland. Prostate-specific antigen examination was within the normal range, and whole-body bone scan examination was normal. In order to clarify the diagnosis, the patient underwent prostate puncture examination and the pathological findings were – prostate specific mesenchymal tumor with undetermined malignant potential. The incidence of prostate-specific mesenchymal tumors is very rare in the clinic, and the incidence of prostate-specific mesenchymal tumors is very low, accounting for less than 0.1% of malignant tumors of the prostate, and there is no unified standard treatment plan. The majority of prostate-specific mesenchymal tumors have a low incidence, accounting for less than 0.1% of prostate malignancies. The majority of prostate-specific mesenchymal tumors are not very aggressive, but there are still some prostate-specific mesenchymal tumors that develop postoperative peripheral metastases and malignantly become prostate mesenchymal sarcoma.