Photothermal ablation has provided emerging and promising opportunities to further potentiate the efficacy of postoperative chemotherapy of tumor. However, it still cannot achieve a high level of selectivity because extraneous photodamage along the optical path to the tumor is unavoidable as the result of the uncontrollable distribution of the photothermal agents. In addition, it is technically difficult to keep photoirradiation localizing only on cancer cells. In this report, a new strategy is introduced for precisely controlled ablation of tumor through tumor microenvironment activated near-infrared (NIR) photothermal therapy. By taking advantage of the pH-dependent light-heat conversion property of Au@PANI nanoparticles, much higher photothermal effect at pH 6.5 than that at pH 7.4 is achieved. Therefore, in normal tissues and blood vessels, NIR irradiation cannot lead to a lethal temperature with little or no harm to normal cells. In contrast, in acidic tumor microenvironment, the photothermal effect is activated. Consequently, NIR irradiation can effectively kill cancer cells through local hyperthermia. Importantly, with the benefit of the internal and external control to switch on the photothermal ablation, the technical difficulty to precisely localize laser irradiation on tumor cells can be circumvented.