To investigate whether concurrent Tislelizumab with postoperative chemoradiotherapy would have survival benefit in high Risk HNSCC Patients.

Inclusion Criteria:

1. Histologically confirmed squamous cell carcinoma of the head and neck. Site of tumor origin in the oral cavity, oropharynx (p16-), larynx, or hypopharynx
2. With at least one high risk factor after radical surgery ①positive margin; ②close margin（<5mm); ③ENE.
3. No distant metastases
4. No synchronous or concurrent head and neck primary tumors
5. ECOG PS 0-1
6. Adequate organ function including the following:

Absolute neutrophil count (ANC) >= 1.5 * 10^9/l Platelets count >= 80 * 10^9/l Hemoglobin >= 80 g/dl AST and ALT <= 2.5 times institutional upper limit of normal (ULN) Total bilirubin <= 1.5 times institutional ULN Creatinine clearance >30 ml/min 8. Signed written informed consent

Exclusion Criteria:

1. Prior chemotherapy or anti-cancer biologic therapy for any type of cancer, or prior radiotherapy to the head and neck region
2. Other previous cancer, except for in situ cervical cancer and cutaneous basal cell carcinoma
3. Pregnant or breast-feeding females, or females and males of childbearing potential not taking adequate contraceptive measures
4. Uncontrolled concomitant illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, or cardiac arrhythmia
5. Active, known or suspected autoimmune disease such as interstitial pneumonia, uveitis, Crohn's disease, autoimmune thyroiditis. Subjects with cured childhood asthma, type I diabetes mellitus and hypothyroidism only requiring hormone replacement, or skin disorders (such as vitiligo, psoriasis, or alopecia) not requiring systemic treatment
6. Using systemic immunosuppressive agents and continue the dose within 2 weeks prior to the enrollment;