In order to study the effects of polarization state and effective numerical aperture on the focal full-width at half-maximum （FWHM） and evanescent depth in confocal total internal reflection Microscopy(CTIRM), according to the Richard-Wolf theory, the intensity distribution in the interface is calculated and discussed with linearly, circularly, radially and azimuthally polarized beams, respectively. Meanwhile, the numerical calculations of FWHM and depth are researched for three different effective numerical apertures (1.33~1.45, 1~1.45 and 1~1.12, respectively). The results indicate that the FWHM of radially polarized beam is 144 nm, breaking through the limitation of diffraction, which is also better than 330 nm of linearly and 360 nm of circularly polarized ones, by using 532 nm incident wave and 1.33~1.45 aperture. The sharper focuscan be got with the larger and thinner aperture. Also the smaller depth of transmission can be got with the larger difference of squares of upper and lower limits, for which 140 nm is the shallowest depth with 1~1.45 aperture. Compared to other polarizations, radially polarized beam is the most suitable choice for CTIRM. And by optimizing the effective numerical aperture, high horizontal resolutions and low axial fluorescent noise near the sample surfacecan be obtained simultaneously.