Objective: To investigate the mechanism of action of the Notch-1/IRE1/XBP1s signaling pathway in diffuse large B -cell lymphoma (DLBCL). Methods: The expressions of relevant proteins were detected by Western blotting. The effect of myeloidspecific knockout of Notch -1 on lymphoma progression was observed by mouse tumor transplantation and imaging. The apoptosis of chimeric antigen receptor T -cell therapy (CAR -T) cells were detected by flow cytometry, and the proliferation of CAR -T cells was detected by wound healing assay and cell counting kit -8 (CCK8) assay. Results: Lymphoma cells mediated the Notch -1 signaling pathway in bone marrow -derived macrophages and promoted the activation of STAT3 and STAT6 in bone marrow -derived macrophages. Myeloid -specific knockout of Notch -1 could inhibit the progression of lymphoma. Lymphoma cells enhanced the expression of p -PERK, p-IRE1 alpha, ATF6, IL -6, IL -4, p-AKT, CD9, CD63 and PD -L1 in bone marrow -derived macrophages by mediating the Notch -1 signaling pathway. Knockout of Notch -1 in macrophages alleviated, to some extent, the suppression of killing activity of CAR -T cells, while activation of Notch -1 in macrophages inhibited proliferation and promoted apoptosis of CAR -T cells. The PD -L1 antibody significantly restored the cytotoxicity and proliferation of CAR -T cells, and inhibited their apoptosis. Conclusion: Activation of the Notch-1/IRE1/XBP1s signaling pathway in myeloid macrophages promotes the secretion of IL -6 and IL -4 as well as PD -L1, thereby inhibiting the activity and proliferation of CAR -T cells and promoting their apoptosis.