Inclusion Criteria:  Patients or their family members agree to participate in the study and sign the informed consent form;  Patients ≥ 18 and ≤75 years old, male or female;  ECOG performance status of 0 or 1;  Patients with histologically confirmed rectal adenocarcinoma;  The clinical diagnosis of chest CT, abdomen and enhanced MRI was cT3/T4a, Nany, M0;  The distance between the lower edge of the tumor and the anal edge is less than or equal to 10 cm;  No history of immune system diseases;  No history of immunodeficiency, including HIV positive;  No history of other malignancies;  No history of myocarditis;  No history of cardiovascular and cerebrovascular diseases;  No history of thyroid dysfunction;  No history of liver and kidney diseases;  No history of mental illness, no history of Infectious diseases;  No history of organ transplantation or allogeneic bone marrow transplantation;  There is no history of other systemic diseases other than the above diseases;  Voluntarily accept the neoadjuvant treatment scheme of radiotherapy, sequential chemotherapy / chemotherapy combined with immunotherapy;  Swallowing pills normally;  Rectal cancer without radiotherapy, chemotherapy, surgery, Chinese medicine anti-tumor treatment, etc.;  Surgical treatment is planned after neoadjuvant treatment.  Exclusion Criteria:  Patients who do not meet the above inclusion criteria;  Documented history of allergy to study drugs, including any component of Tislelizumab, capecitabine, oxaliplatin and other platinum drugs;  Patients who need to be treated with corticosteroid (dose equivalent to prednisone of >10 mg/day) or other immunosuppressive agents within 2 weeks prior to study drug administration; Major surgery or severe trauma within 4 weeks before the first use of the study drug;  Severe infection (CTCAE > 2) occurred within 4 weeks before the first use of the study drug; Baseline chest imaging revealed active pulmonary inflammation, signs and symptoms of infection within 14 days prior to the first use of the study drug, or oral or intravenous antibiotic therapy, except for prophylactic use of antibiotics;  Female patients who is pregnant or breastfeeding;  Patients who refuse to sign informed consent by themselves or their authorized persons;  Patients with poor cognitive ability, unable to answer questions, unable to fill in questionnaires or mental disorders;  Patients considered unsuitable for the study by the investigator.