This study will evaluate the efficacy and safety of SHR-1701 combined with radiotherapy and chemotherapy as perioperative treatment for locally advanced rectal cancer. Eligible patients will receive standard chemoradiation with SHR-1701 followed by XELOX combined with SHR-1701. In all subjects, restaging pelvic MRI with chest and abdominal CT will be performed after completion of neoadjuvant treatment to determine resectability and to rule out any evidence of metastases. Subjects who have resectable disease will undergo surgery. Adjuvant XELOX combined with SHR-1701 will be given after surgery.

Inclusion Criteria:

1. Be willing and able to provide written informed consent for the trial.
2. Locally advanced rectal adenocarcinoma and was evaluated as resectable ;
3. The inferior margin of the tumor ≤ 10 cm from the anal verge ;
4. No prior anti-cancer treatment for rectal cancer;
5. Estern Cooperative Oncology Group (ECOG) Performance status (PS) of 0 or 1;
6. Adequate hematologic and end-organ function;
7. Contraception was initiated from the signing of the informed consent until at least 6 months after the last dosing of the study drug

Exclusion Criteria:

1. Unresectable disease determined by investigators
2. Recurrent rectal cancer
3. Evidence of metastatic disease or lateral lymph node metastases
4. Presence of synchronous colorectal cancer
5. Presence of obstruction or imminent obstruction
6. Not eligible for long-course radiotherapy
7. Severe cardiovascular and cerebrovascular diseases;Have clinical heart symptoms or diseases that are not well controlled
8. Prior malignancy within the prior 5 years. Exceptions include basal cell carcinoma of the skin or squamous cell carcinoma of the skin that has undergone potentially curative therapy or in situ cervical/breast cancer.