Objective To construct a humanized-immune-system mouse model with human pancreatic cancer and evaluate its effectiveness in order to provide an ideal preclinical animal model for pancreatic cancer immunotherapy research. Methods Ficoll density gradient centrifugation was used to isolate fresh peripheral blood mononuclear cells (PBMC) from healthy people. The cells were injected into the tail vein of severe combined immunodeficiency NOD/ ShiltJ- Prkdc em26Cd52 Il2rg em26Cd22 ( NCG) mice to construct a model with a humanized immune system. We then subcutaneously implanted human pancreatic cancer Aspc1 cells into the mice and regularly monitored tumor growth. Three weeks later, the peripheral blood of the reconstructed mice was collected for flow cytometric analysis to detect the levels of human CD45⁺ cells. When the tumors grew to 100 ~ 200 mm³ , immunotherapy with human anti-PD-1 monoclonal antibody was started. After continuous treatment for 3 weeks, the mice were euthanized, and samples taken. Flow cytometry, immunohistochemistry, and other method were used to analyze the infiltration and activation of human immune cells in the peripheral blood, spleen, bone marrow, and tumor tissues of the humanized-immune-system mice with human pancreatic cancer. Results Three weeks after implantation of human PBMC, high levels of human CD45⁺ cells were detected in the peripheral blood, spleen, and bone marrow of the mice. The reconstructed humanized immune system inhibited the growth of human tumors (P< 0.01, P< 0.001) and was activated by human anti-PD-1 monoclonal antibody to promote cytotoxic CD8⁺ T cell infiltration and PD-L1 expression in the tumor tissues. Conclusions A humanized immune system mouse model with human pancreatic cancer was successfully constructed. The reconstructed humanized immune system responded well to human anti-PD-1 monoclonal antibodies and restrained the growth of human pancreatic tumor cells. Thus, this study has provided an ideal preclinical animal model of immunotherapy for pancreatic cancer.