The vacuum packaged cantilever with a small magnet is fabricated successfully, and applied to map the magnetic field and radical density at the ambient atmosphere based on magnetic force sensing. The 1.5-μm-thick Si cantilever with a 20-μm-diameter of Nd-Fe-B particle is packaged in a vacuum cavity using an anodic-bonding technique. Before the final bonding process, the relationship of the quality (Q) factor of cantilever with pressure is calibrated. After vacuum packaging, the pressure is determined to be in the range of 7.3×102 ∼ 1.0×103 Pa. The force sensitivity is estimated to be 1.1×10-13 N/√Hz. The magnetic fields with a resolution of ∼4.0×10-6 and ∼2.4×10-10 T are detected by measuring the variations of the resonant frequency and resonant amplitude of the cantilever, respectively. Also, the magnetic force caused by electron spin resonance (ESR) of a standard radical polymer, DPPH, is demonstrated at atmospheric environment.