Triple-negative breast cancer (TNBC) is a kind of aggressive malignancy with fast metastatic behavior. Herein, a nanosystem loaded with a near-infrared (NIR) agent is developed to achieve chemo-photothermal combination therapy for inhibiting tumor growth and metastasis in TNBC. The NIR agent of ultrasmall sized copper sulfide nanodots with strong NIR light-absorbing capability is entrapped into the doxorubicin-contained temperature-sensitive polymer-based nanosystem by a self-assembled method. The temperature sensitive nanoclusters (TSNCs) can significantly enhance the drug penetration depth and significantly kill the cancer cells under the near-infrared laser irradiation. Importantly, it is plausible that the tumor penetrating nanosystem combined with NIR laser irradiation can prevent lung and liver metastasis via extermination of the cancer stem cells. The in vivo characteristics, evaluated by photoacoustic imaging, pharmacokinetics, and biodistribution, confirm their feasibility for tumor treatment owing to their long blood circulation time and high tumor uptake. Thanks to the high tumor uptake and highly potent antitumor efficacy, the doxorubicin-induced cardiotoxicity can be avoided when the TSNC is used. Taken together, it is believed that the nanosystem has excellent potential for clinical translation.