Specific tumor-responsive capabilities and efficient synergistic therapeutic performance are the keys to effective tumor treatment. Herein, AuNRs@SiO2-RB@MnO2 was developed as a new type of tumor-responsive nanotheranostic for multimodal imaging and synergistic chemodynamic/photothermal therapy. In AuNRs@SiO2-RB@MnO2, the SiO2 layer wraps the AuNRs, providing light absorption in the second near-infrared (NIR-II) region. The SiO2 layer also adsorbs the MnO2 nanosheets, which have Fenton-like activity, resulting in a fluorescent sensing platform based on the fluorescence quenching properties of MnO2 for rhodamine B dye. The fluorescence can be recovered by the consumption of MnO2 by glutathione, which simultaneously produces Mn2+ in the tumor region. The recovery of fluorescence reflects the consumption of glutathione and the increase in Mn2+, which produces hydroxyl radicals via Fenton-like reaction in the tumor microenvironment to realize chemodynamic therapy. Meanwhile, the AuNRs are a good photothermal reagent that can effectively absorb NIR-II light and convert it into heat energy to kill tumor cells via photothermal therapy. The NIR-II absorption performance of the AuNRs provides good photoacoustic imaging and deep photothermal performance, which is favorable for efficient NIR-II photoacoustic imaging-guided photothermal therapy. As a result, the AuNRs@SiO2-RB@MnO2 nanotheranostic exhibits outstanding imaging and synergistic chemodynamic/photothermal therapeutic performance for tumor imaging and treatment.