High sensitivity magnetic sensing is proposed using a sandwich structure with polydimethylsiloxane (PDMS) flexible resonator as the core. The directional sensing feature is provided by the sandwich structure’s preset magnetic field. The small Young’s modulus of flexible material corresponds to larger variation, resulting in a highly sensitive magnetic response. In the unshielded environment, the experimental results demonstrate redshift sensitivity of 1.08 nm / mT and blueshift sensitivity of 1.12 nm / mT, which are attributed to a slight variation in the PDMS’s Young’s modulus. The directivity curve’s concave point has a depth of 34.6 dB. The minimum detectable magnetic field of 0.96 nT · Hz ^{− 1/2} is achieved at 1.4 kHz.