This study is intended to evaluate efficacy and safety of the combination of regorafenib and nivolumab as third-line or later therapy in patients with microsatellite stable (MSS) colorectal cancer (CRC).

Inclusion Criteria:

• Advanced Colorectal Cancer diagnosed histologically;
• Patients with microsatellite stable (MSS)
• Patients have no any standard choice after multiple line of therapy( ≥ 2 lines);
• Expected survival ≥ 3 month;
• ECOG / PS score: 0-2, and the main organ function to meet the following criteria: HB ≥ 90g / L, ANC ≥ 1.5 × 109 / L, PLT ≥ 80 × 109 / L,BIL <1.5 times the upper limit of normal (ULN); Liver ALT and AST <2.5 × ULN and if liver metastases, ALT and AST <5 × ULN; Serum Cr ≤ 1 × ULN, endogenous creatinine clearance ≥50ml/min

Exclusion Criteria:

• Patient still has standard treatment therapy based on NCCN guidance;
• Patient can not comply with research program requirements or follow-up;