Photon Scanning Tunneling Microscope (PSTM) is a near-field optical microscope that can measure local optical properties with high resolution beyond the diffraction limit and was widely applied in practices in recent years. The resolution of PSTM, which mainly depends on the shape of the taper tip, is an important issue to be discussed in the application. In this paper, the near-field distribution around a new PSTM probe is simulated by the method of 3-D Finite-Difference Time-Domain (FDTD). In this model, a nanometric metallic pyramid is attached at the apex of the metal-coated probe. Considering the interaction between the sample and the probe tip, the near-field distribution in a section at certain height is plotted as a function of the various sample positions. In order to optimize the optical property of this kind of optic fiber probe tip, the influence of the parameters of the taper tip can also be studied. To understand the effect of the probe film and the metal tip, the electromagnetic field distribution in the vicinities of the sample and the fiber probe during the third period is plotted. Thus, these simulated results offer references for the selection of the probe shape in experiments.