Carcinosarcoma, also known as malignant Mullerian mixed tumour, is a rare and aggressive ovarian malignant tumour. The prognosis of ovarian carcinosarcoma is very poor, accounting for the vast majority of ovarian cancer deaths. Due to the rarity of ovarian carcinosarcoma, no unified treatment plan exists at present. Here, we report the case of a 69-year-old patient with stage IC ovarian carcinosarcoma. She underwent right salpingo-oophorectomy and R0 resection, inclouding extrafascial hysterectomy, left salpingo-oophorectomy, omentectomy, appendectomy, right pelvic lymph node dissection and multipoint biopsy. Full-exome sequencing was performed with normal ovarian tissue, cancer tissue, sarcoma tissue and carcinosarcoma tissue, and the results showed that the sarcoma and carcinosarcoma tissue shared more mutated genes. A TP53 mutation occurred in the cancer tissue and carcinosarcoma tissue. By analysing the lychee tree, we found that the sarcoma tissue and carcinosarcoma tissue shared more subclones and determined that they were more closely related; the cancer tissue carried fewer subclones and was the main clone. The sarcoma may have evolved from the cancer tissues. Six rounds of postoperative chemotherapy (carboplatin + paclitaxel + ifosfamide (IFO) (paclitaxel 200 mg, D1 + carboplatin 600 mg, D1 + IFO 2G, D1-D3)) were administered. The patient has been followed up for six years and is currently in good health. In conclusion, the disease was diagnosed in the early stage, and the use of a R0 resection + a three-drug combination chemotherapy may have contributed to the patient's long-term disease-free survival. The results of the gene study suggested that the sarcoma component may be differentiated from the cancer component. We thus speculated that the origin of this case may have been the fallopian tube.