BACKGROUND: Non-small cell lung cancer (NSCLC) is the most common type of lung cancer. Tumor treating fields (TTFields) combined with anti-PD immunotherapy offers a promising strategy to address this issue. Nevertheless, the mechanism of action (MOA) of TTFields therapy combined with anti-PD immunotherapy in NSCLC has not been thoroughly investigated. This study aims to elucidate the MOA of the combined therapy from the aspect of improving the tumor immune microenvironment (TIME). METHODS: Using a mouse model of NSCLC, we tested the efficacy of TTFields therapy with anti-PD-1 and anti-PD-L1 immunotherapy. By RNA-seq, the differential genes and signaling pathways between combination therapy and anti-PD therapy groups were studied. In-vitro experiments validated the effects of TTFields on tumor cells for CD4 T cell and CD8 T cell infiltration, as well as the expression of tumor immunogenic death related genes and chemokines. RESULTS: Combining TTFields with anti-PD-1 reduced tumor weight and volume, respectively, compared to controls (p < 0.05). RNA-seq analysis revealed 1,745 differentially expressed genes (DEGs) in the combination therapy group versus controls, including upregulated immune pathways and immunogenic cell death (ICD) associated genes. Further study showed that the combination therapy resulted in increased T cell infiltration compared to anti-PD immunotherapy alone, and TTFields induced higher level expression of ATP, HMGB1, CCL2, CCL8, CXCL9, and CXCL10 and inflammatory cytokines than control group. These effects collectively contributed to the altered TIME, and finally potentiated the efficacy of anti-PD therapy. CONCLUSIONS: TTFields enhance the effectiveness of anti-PD immunotherapy by improving CD4 T cells and CD8 T infiltration via inducing ICD to increase CCL2/8 and CXCL9/CXCL10 expression of tumor cells. This study provides theoretical basis and new insights for evaluating the effectiveness of TTFields combined with anti-PD therapy for NSCLC.