Abstract: Tumors are one of the leading causes of death in the world, and achieving precise and non-invasive efficient diagnosis and treatment of tumors is of great significance. We used carbon nanotubes (CNTs) with extremely high aspect ratio, easy to penetrate cell membrane and excellent biocompatibility as carriers, and acetylacetone iron as iron source, to synthesize magnetic carbon nanotube composite nanomaterials with excellent water dispersion stability by in situ growing superparamagnetic ferric oxide nanoparticles (Fe₃O₄ NPs) on their surface through solvothermal method. The results showed that the magnetic carbon nanotubes had high near-infrared photothermal conversion performance, and could reach 48.6℃ in 10 min under 808 nm laser irradiation at a concentration of 50 μg·mL⁻¹, and had good photothermal stability. Cell and imaging experiments showed that the composite nanomaterials had good biocompatibility and excellent photothermal killing effect on human cervical cancer cells (HeLa). In vitro simulated tumor microenvironment, the magnetic resonance imaging (MRI) T₂ relaxation rate r₂ of the magnetic carbon nanotubes was up to 215.61 mmol⁻¹·L·s⁻¹, indicating that the prepared magnetic carbon nanotubes had outstanding biosafety, magnetism and photothermal properties, and were expected to be applied to the integration of magnetic targeted tumor photothermal therapy and magnetic resonance imaging.