Magnetic nanomaterials with small coercivity have a potential application related to the dynamic magnetization including magnetic hyperthermia (kHz) and microwave devices (GHz). One-dimensional (1D) magnetic nanostructures with the high aspect ratio have drawn considerable attention due to their control on the magnetic moment reversal by the large shape anisotropy. Herein, we propose a facile approach to obtain well-dispersed highly crystalline Fe3O4 nanorods (NRs) by the solvent-thermal method. The aspect ratios of Fe3O4 NRs can be tuned from 4.5 to 10. Magnetic induction fields within and around a single Fe3O4 nanorod in the remanence state were obtained by off-axis electron holography. The induction fields indicated a single domain state of the highly anisotropic Fe3O4 nanorod due to its strong magnetic shape anisotropy. Quantitative magnetic moment analysis of the obtained phase image yielded an average magnetization of 0.53 T of a single Fe3O4 nanorod. We demonstrate that the specific absorption rate (SAR) of Fe3O4 NRs with an aspect ratio of 4.5 can be enhanced by tuning have a much higher SAR as compared with 15 nm Fe3O4 nanoparticles and Fe3O4 NRs counterparts with an aspect ratio of 10. The highest SAR is greatly increased up to 1072 W g−1 for an AC field of 33 kA m−1 and a concentration of 5 mg mL−1. These findings provide a new strategy to improve the heating efficiency of magnetic nanomaterials at the lower particles concentration with minimal invasiveness for the patient. Moreover, Moreover, the real part of the permeability (μ’) of magnetic-oriented Fe3O4 NRs is obviously higher than that of random Fe3O4 NRs in the GHz range. The oriented Fe3O4 NRs exhibit a higher resonance peak at 4.75 GHz compared to the bulk counterpart (1.2 GHz) in the frequency dependence of μ in the range of 1–10 GHz. These results could play a guiding significance in the development of an effective method to improve the permeability of magnetic nanomaterials at GHz working frequency.