Bessel beam generated by lens-annular slit system is analyzed in discrete Fourier transform method. In the theoretical part, Kirchhoff diffraction integral formula and Fresnel diffraction integral formula are expressed in the form of Fourier transform, the complex amplitude distribution of each surface is described in Fourier method. After collating and sampling, a discrete Fourier formula is derived to describe the intensity distribution of observation surface which has function relation with diffraction surface. After setting related parameters and simulating with MATLAB, the results show the intensity distribution of Bessel beam in different propagation distances. At last, an experimental system is designed to verify the theoretical analysis and numerical simulation. Simulation results and pictures from experiment show a higher match degree, which proves that this discrete Fourier transform method is feasible in lens-annular slit system.