A single-arm, open-label clinical study of irinotecan liposome combined with capecitabine, bevacizumab and camrelizumab as second-line or above treatment for patients with metastatic colorectal cancer, aiming to evaluate the efficacy and safety of irinotecan liposome combined with capecitabine, bevacizumab and camrelizumab as second-line or above treatment for patients with metastatic colorectal cancer The medication regimen is irinotecan liposome (II) + capecitabine + bevacizumab + camrelizumab until disease progression or intolerable toxicity.