A near-field trapping method for nanoparticles by a metal-coated optical fiber probe is proposed to improve the nanomanipulation technology. By applying a Maxwell stress tensor and 3D Finite Difference Time Domain(FDTD) methods,the physical properties of trapping stability,particle sizes and trapping positions in the near-field trapping are revealed. The effect of trapping forces acted on a nanoparticle along three axis directions on the trapping positions is studied, and different trapping positions are generated in the aperture edge in polarization direction and the center surface of the probe tip. Numerical results indicate that the Near-field Scanning Optical Microscopy (NSOM) probe is able to trap nanoparticles in a circular shape with lower laser intensity (~1040 W/mm2) than that (~105 W/mm2) required by a conventional optical manipulator. A near-field optical trapping system using the tapered metal-coated fiber probe is designed. A NSOM probe, a polarized semiconductor laser and a laser scanning confocal microscope are applied to pushing the trapping resolution further down to 120 nm. In experiments, 120-nm polystyrene particles are trapped in multi-circular shape with a minimum size of 400 nm at a resolution of λ/7 (λ: laser wavelength) and d (d: tip diameter of NSOM probe), respectively,which agrees well with the simulated result. The method proposed in the paper largely promotes the role of near-field optical manipulation.