In immunotherapy, 'cold' tumors, with low T cells infiltration, hardly benefit from the treatment of immune checkpoint inhibitors (ICIs). To address this issue, we screened two 'cold' tumor models for mice with high expression of galectin-3 (Gal-3) and designed a cocktail strategy to actively recruit CD8+ T cells into the tumor microenvironment (TME), which reversed 'cold' tumors into 'hot' and remarkably elevated their ICIs-responsiveness. Gal-3, an important driving force of tumorigenesis, inhibits T cell infiltration into tumor tissue that shapes 'cold' tumor phenotype, and promotes tumor metastasis. In this respect, Gal-3 antagonist G3-C12 peptide was chosen and further loaded into poly(lactic-co-glycolic acid) (PLGA) microspheres, with the prepared G3-C12@PLGA playing a dual role of antitumor, namely, killing two birds with one stone. Specifically, G3-C12@PLGA actively recruit T cells into 'cold' tumors by rescuing IFN-γ, and simultaneously inhibit tumor metastasis induced by Gal-3. Moreover, when combined with chemotherapeutic agent (Oxaliplatin) and anti-PD-1 peptide (APP), the immunopotentiating effect of dendritic cells (DCs) was extremely improved, with T-cell depletion dramatically reversed. In vivo experiments showed that such cocktail therapy exerted remarkable antitumor effect on 'cold' breast cancer (BC) and ovarian serous cancer (OSC). These results indicated that our strategy might be promising in treating 'cold' tumors with high expression of Gal-3, which not only enhance cancer treatment outcome, but provide a new platform for the prevention of postoperative tumor recurrence/metastasis.