The goal of this clinical trial is to assess the 1-year DFS rate of toripalimab adjuvant therapy in participants with resected esophageal squamous cell carcinoma (ESCC) who achieved pCR. The main questions it aims to answer are:

• The toripalimab adjuvant therapy could impove the 1-year DFS rate in participants with rescted ESCC who achieved pCR?
• Is this treatment regimen safe? Researchers will compare toripalimab adjuvant therapy to clinical observation to see if toripalimab could improve the 1-year DFS rate.

Participants will receive toripalimab 240 mg IV once every 3 weeks for one year or clinical observation.

Inclusion Criteria:

• Stage II or III esophageal cancer with histologically confirmed predominant squamous cell carcinoma at initial diagnosis;
• Subjects must complete preoperative neoadjuvant therapy (unlimited treatment regimen) before being assigned to treatment and then undergo surgery;
• Subjects must undergo complete resection (R0), be surgically determined to be disease-free and have a negative margin on the resected specimen, defined as no viable tumor within 1 mm of the proximal, distal, or surrounding resection boundary;
• Subjects must have no residual pathology, the primary tumor is pCR, and the pathology report of the resected lymph nodes is ypN0;
• ECOG performance status of 0 or 1;
• The laboratory test meet the following requirements:

Bone marrow function: neutrophils ≥ 1.5×10(9)/L, platelets ≥ 100×10(9)/L, hemoglobin ≥ 90 g/L Liver function：Total bilirubin ≤ 1.5 x ULN；AST and ALT ≤ 3 x ULN Renal function：Cr ≤ 1.5 x ULN，Ccr ≥ 50 ml/min.

Exclusion Criteria:

• Subjects with stage M1 resectable disease；
• Received treatments for resected esophageal cancer (e.g., immunotherapy , chemotherapy, targeted therapy, radiotherapy, or biologic therapy);
• Known to be allergic, highly sensitive or intolerable to research-related drugs or excipient
• In the past 5 years, there were other malignant tumors, melanoma skin cancer or ervical carcinoma in situ were excepted.