A plasmonic fiber-tip based on the metallic metasurface and the multimode fiber (MMF) alleviates the limitation of the inevitable large sensing size caused by fiber side wall functionalization. Localized surface plasmon resonance (LSPR) based on metasurface on the fiber-tip provides a promising way to manipulate and interrogate the transmitted and reflection light in sub-wavelength range. Combining the advantages of plasmonic fiber-tip and magnetic fluid, a compact magnetic field fiber-optic sensor is proposed and verified by experiments. The developed fiber-optic magnetic field sensor has linear response and high magnetic strength sensitivity of 0.532 nm/mT over a range of 0-20 mT. In addition, the results also prove the feasibility of pseudo-vector magnetic field sensing.