Imaging-guided chemo-phototherapy based on multifunctional nanocarriers has emerged as a promising and high-efficient cancer treatment because of the inevitable limitations of single therapy. Herein, a near-infrared (NIR) light-activated degradable polymeric nanoplatform was fabricated for chemo-phototherapy. An NIR photosensitizer, IR780, and a chemotherapeutic drug, doxorubicin (DOX), were efficiently coloaded within a reactive oxygen species (ROS)-sensitive polymeric micelle based on an amphiphilic copolymer with degradable thioketal (TK) linkages. The obtained spherical nanoparticles (denoted as (IR780/DOX)@PTK) exhibited a notable photodynamic and photothermal effect upon NIR light exposure. Furthermore, due to the rapid cleavage of TK linkers induced by ROS generated from NIR-activated IR780, (IR780/DOX)@PTK also showed an NIR light-induced degradable feature, which can be used for light-triggered tumor-specific drug release and lead to ignorable systematic toxicity after biodegradation and drug delivery. Under the guidance of NIR fluorescence and photothermal dual modal imaging, (IR780/DOX)@PTK exhibited excellent tumor accumulation after intravenously injection into 4T1-tumor-bearing mice. As verified in both in vitro and in vivo study, (IR780/DOX)@PTK presented a significant tumor suppression effect by synergistic chemo-phototherapy.