Precise oncotherapy requires effective cancer treatments that are guided by clinical imaging techniques. One of the most representative cases is multi-imaging-guided phototherapy. This study presents a novel multifunctional theranostic agent of SnxWO3 tungsten bronze, which is an excellent light absorber in the near infrared (NIR) range. Theoretical calculations based on density functional theory confirm that the insertion of donor Sn atoms into orthorhombic WO3 gives rise to the broadband visible-NIR absorption. Accordingly, both the photothermal effect and reactive oxygen species (ROS) production could be realized under NIR light irradiation by SnxWO3 tungsten bronze nanocrystals, thereby triggering the potent in vivo photothermal and photodynamic synergistic therapy. Meanwhile, modified SnxWO3 tungsten bronze has the functions of photoacoustic imaging (PAI), X-ray computed tomography (CT) imaging and near-infrared fluorescence (NIRF) imaging for tumor detection as well. Finally, for investigating the antitumor mechanism of in vivo solid tumors, clinical imaging modalities of B-mode ultrasonography (US) and magnetic resonance imaging (MRI) are employed to monitor the tumor evolution process after the photo-treatment, verifying a typically liquefactive necrosis process. These results indicate that the SnxWO3 tungsten bronze nanostructure is a promising theranostic agent for imaging-guided cancer therapy.