Postoperative CCRT Followed by Immunotherapy in High-Risk LA HNSCC

Inclusion Criteria: * Histologically proven squamous cell carcinoma of the head and neck which include but not limit following primary sites: oral cavity, oropharynx, hypopharynx or larynx * Patients eligible with one or more High-Risk factors of the following: For HPV+ OPSCC: T4 OR cN3 OR pN2 OR non-R0 resection OR resection margin\<5mm OR ENE (+) OR perineural invasion OR vessel/lymphatic vessel invasion；For HPV- HNSCC：T4 OR cN3 OR pN2 OR non-R0 resection OR resection margin\<5mm OR ENE (+) OR perineural invasion OR vessel/lymphatic vessel invasion OR IV/V cervical lymph node metastases * ECOG performance score 0-1 * PD-L1 expression with CPS\>1 * No contraindications to immunotherapy or chemoradiotherapy * Adequate organ function * Female subject of childbearing potential should have a negative pregnancy test within 7 days prior to receiving the first dose of study medication.Female subjects of childbearing potential must be willing to use an adequate method of contraception during the course of the study and 60 days after the last dose of study medication. * Reproductive male subjects must agree to use an adequate method of contraception during the course of the study and 60 days after the last dose of study medication. * Informed consent is obtainable. Exclusion Criteria: * Previous or co-existing malignancies, except cured basal cell carcinoma of the skin, cervical carcinoma in situ, superficial bladder cancer * Active infection * Known active viral infection Human Immunodeficiency Virus (HIV), Hepatitis B/C) or known history of positive test for HIV * Active and/or historical autoimmune disease, except patients with vitiligo or asthma that has completely resolved in childhood and does not require any intervention in adulthood * Clinically significant (i.e., active) cardiovascular disease: cerebral vascular accident/stroke (\< 6 months prior to enrollment), myocardial infarction (\< 6 months prior to enrollment), unstable angina, congestive heart failure (≥ New York Heart Association Classification Class II), or serious cardiac arrhythmia requiring medication * Pregnant, breastfeeding patients, and female patients of childbearing potential who are unwilling or unable to use 2 highly effective methods of contraception as outlined in the protocol for the duration of the study * History of PD-1/L1 treatment * If the subjects underwent major surgery for non-tumors, the toxicity and complications of the surgery needed to be adequately treated and the body conditions returned to normal * Concurrent enrollment in another clinical trial using an investigational anti-cancer treatment within 28 days prior to the first dose of study treatment * Other circumstances leading to the termination of the study, as determined by the investigator