The focusing properties of plane wave,Gaussian beam,Bessel-Gaussian beam and double-ring Laguerre-Gaussian beam are studied using theoretical calculation m ethod. The rules of focal intensity distribution and radius of center dark area are ana lyzed with the variations of numerical aperture and truncation parameter.Through theo retic analysis and calculation,the rules of using central obscuration aperture to inc rease depth of focus and reduce the radius of central dark area are also analyzed. Researches find that the radii of central dark area formed by 4kinds of light beams in the focal plane are monotonically decreasing,which are inversely propor tional to the numerical aperture and proportional to the wavelength.The change of truncation factor has more influence on the radius of central dark area while ha s little effect on the sidelobe intensity which is formed by Gaussian beam or Bessel-Gaussian b eam.Optical intensity distribution in focal plane formed by double-ring azimuthally Laguerr e Gauss beam can be redistributed with the variety of truncation factor.A double ring structure which has equal intensity can be formed in the focal plane.Using the c entral obscuration aperture,the radius of central dark area in focal plane can be redu ced and the depth of focus can be increased.Research results may have quite important applications for azimuthally polarized light.