Carrier-free nanodrugs composed of photosensitizers and chemotherapeutic drugs show great potential in synergistic photothermal-chemotherapy. However, the targeting specificity to tumor cells is still a major obstacle for carrier-free nanodrugs. Meanwhile, almost all exogenous tumor-targeting ligands show no therapeutic effect by themselves. Here, a tumor microenvironment-driven self-targeting supramolecular nanodrug was successfully constructed via an indocyanine green (ICG)-templated small-molecule self-assembly strategy with methotrexate (MTX, folic acid-like antitumor drug) followed by post-insertion of weak acidity-responsive PEG for synergistic photothermal-chemotherapy. Interestingly, the size and morphology could be adjusted by changing the ICG-to-MTX ratio. Notably, the dynamic introduction of PEG not only could temporarily shield self-targeting function in blood to prolong the circulation time, but also could trigger the activation of self-targeting via re-exposing MTX ligands within the tumor microenvironment to enhance cellular uptake. Furthermore, the dePEGylated nanodrug would be disassembled to release MTX on-demand for chemotherapy via both stimuli of stronger lysosomal acidity and an external NIR laser. Moreover, the elimination of tumors could be realized through NIR-II fluorescence/PA imaging-guided synergistic photothermal-chemotherapy. The tumor microenvironment-driven carrier-free nanodrug based on self-targeting activation via ICG-templated assembly might provide a brand-new idea for synergistic photothermal-chemotherapy.