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Lack of biopsies after treatment, especially in solid tumors, restricts the understanding of chimeric antigen receptor (CAR)-T cells -related characteristic in vivo, thus hindering the development of strategies to improve CAR-T cells efficacy. Here, we applied nineteen individual single-cell RNA sequencing (scRNA-seq) data from clinical samples of digestive cancers to explore the characteristics of tumor-infiltrating T cells (TILs) to identify effective targets which might be benefit for enhancing the function of CAR-T cells. The data showed that natural killer cell granule protein 7 (NKG7) was overexpressed in TILs and positively associated with anti-PD1 or anti-CTLA4 therapy in digestive cancers. Subsequently, we found that ectopic expression of NKG7 significantly improved the cytotoxicity of B7H3-targeting CAR-T cells to B7H3-positive digestive cancer cells (MKN45, Huh7, HuCCT-1, SW620 and PANC-1 cells), as well as promoted the TNF-α and IL-2 expression. Furthermore, in a CD19-targeting CAR-T model, the therapeutic efficacy was also found increased after NKG7 overexpression. Mechanically, NKG7 preserved surface CAR expression and promoted CAR-T cell proliferation after exposing to relative tumor antigen. These results indicated that it may be feasible to explore single-cell sequencing data of clinical tumor samples to find strategies to improve CAR-T function, and that ectopic expression of NKG7 is an effective strategy to improve the therapeutic efficacy of CAR-T cells against tumors.