Herein, a novel tumor microenvironment (TME)-mediated nanotheranostics platform of iron oxychloride (FeOCl) nanorods coated with Prussian Blue (PB), polydopamine (PDA), black phosphorus quantum dots (BPQDs) and chelated with Mn2+ was prepared. In the highly integrated nanoplatform (FeOCl@PB@PDA@BPQDs@Mn), FeOCl catalysts exhibit supreme efficiency to yield hydroxyl radicals (•OH) by H2O2 decomposition for chemodynamic therapy (CDT). Moreover, the PB, FeOCl, and Mn2+ have a catalase-like activity that catalyze H2O2 to release of O2 in the TME. Upon laser irradiation, the BPQDs transform O2 to a singlet oxygen (1O2) to self-enhance photodynamic therapy (PDT). Additionally, as a result of the high near-infrared (NIR) absorption rate and efficient photothermal conversion of PB and PDA, FeOCl@PB@PDA@BPQDs@Mn nanocomposites (NCs) are capable to work as ideal theranostic agents for photothermal therapy (PTT) in vitro and in vivo. Furthermore, FeOCl@PB@PDA@BPQDs@Mn NCs can also serve as multimodal imaging agents in different methods, such as magnetic resonance (MR), photoacoustic (PA), and ultrasound (US) imaging. Among the tumor models of mice, CDT, PDT, and PTT that combined with multimodal imaging achieved a more significant synergistic therapeutic result compared to any single treatment modality alone. Therefore, the multifunctional nanosystem in this study possesses tremendous potential in providing a satisfying paradigm for effective tumor treatment.