...1.Pathologically confirmed as colorectal cancer; 2.After radical resection of colorectal cancer; 3.Postoperative pathological staging stage II-III; 4.Confirmed as dMMR-MSI-H; 5.Distant metastasis occurred in postoperative review; 6.Aged 20 to 80 years; 7.ECOG score 0-1 points; 8.White blood cell count>4x10^9/L, platelet count>80x10^9/L, liver and kidney function normal, electrocardiogram normal, no immunotherapy contraindications....