Polymeric micelles have demonstrated wide utility for chemodrug delivery, which however, still suffer from shortcomings such as undesired drug loading, disassembly upon dilution, pre-leakage of drug cargoes during systemic circulation, and lack of cancer-selective drug release. Herein, a poly(ethylene glycol) (PEG)-polyphosphoester-based, reactive oxygen species (ROS)-responsive, core-cross-linked (CCL) micellar system was developed to encapsulate both chemodrug (doxorubicin, Dox) and photosensitizer (chlorin e6, Ce6). The hydrophobic core of the micelles was cross-linked via a thioketal (TK)-containing linker, which notably enhanced the drug loading and micelle stability. In tumor cells, far-red light irradiation of Ce6 generated ROS to cleave the TK linkers and disrupt the micelle cores. As such, micelles were destabilized and Dox release was promoted, which thereafter imparted synergistic anti-cancer effect with ROS-mediated photodynamic therapy. This study provides an effective approach to realize the precise control over drug loading, formulation stability, and cancer-selective drug release using polymeric micelles, and would render promising utilities for the programmed anti-cancer combination therapy.