The surface plasmon resonance (SPR)-based optical fiber tip sensor is more convenient for the chemical or biological sensing since it occupies less space than the SPR-based optical fiber sensor using the transmitted spectrum as the sensing signal. In this work, a detail theoretical analysis for the SPR-based optical fiber tip sensor has been finished. First, the effects of the geometric parameters on the reflecting spectrum, resonance wavelength and sensitivity have been investigated. Then, a dispersion function-based explanation for the relationship between resonance wavelength and tip angle has been presented. It can be seen that the increase of tip angle may lead to the increase of resonance wavelength and the broadening of resonance dip because the incident angle of the ray at the tip interface changes in a greater region.