Rectal cancer is one of the common malignant tumors of the digestive tract. Some patients with rectal cancer are already advanced tumors when they are first diagnosed. At this time, the tumor has local infiltration, the probability of recurrence and metastasis after surgical resection is high, and even radical tumor resection cannot be performed. Neoadjuvant chemotherapy and radiotherapy have become one of the important treatment methods for these patients to increase the rate of radical tumor resection. However, a series of side effects of neoadjuvant radiotherapy can even continue after the end of radiotherapy, and even increase the incidence of postoperative complications. Superselective arterial interventional chemotherapy has been widely used in preoperative neoadjuvant chemotherapy for various tumors, and its efficacy in rectal cancer has also been confirmed. In addition, as a hot spot in tumor treatment, tumor immunotherapy has shown exciting effects in the NICHE study of neoadjuvant immunotherapy before colon cancer surgery. Moreover, Oxaliplatin is a classic chemotherapeutic drug that induces Immunogenic cell death effects, which induce antitumor immunity. Therefore, in order to optimize the preoperative neoadjuvant therapy plan, the investigators propose a treatment method of superselective arterial chemoembolization combined with immunotherapy and systemic chemotherapy, in order to obtain better preoperative conversion therapy effect and reduce the adverse reactions of neoadjuvant therapy.