“Nanotheranostics” has attracted much attention due to the development of nanomaterials with integrated diagnostic and therapeutic functions. In this work, we fabricated a thermal-sensitive nanotheranostic agent, phase-shifted magnetic nanoparticles (PMNPs), which effectively absorbs heat to achieve hyperthermic therapy in response to NIR irradiation, synergistically enhancing tumor therapy via a phase-shift thermoelastic expansion effect, and can be used as a dual-modal contrast agent for US/MR imaging-guided hyperthermia therapy. Histology and electron microscopy confirmed severe cell damage injuries, with fragmentation of lysed cells and nuclear membranes, leaving a mass of vacuoles, and many microbubbles generated with Fe₃O₄ nanoparticles expelled to the edge or outside of the microbubbles, thereby achieving a high concentration dose at the target tissue and minimizing systemic side effects.