Based on the Fresnel diffraction integral,the intensity distribution of Laguerre-Gaussian beam transmitted through a single-slit has been investigated. It is found that the diffraction fringes of vortex beams will dislocation and shift in the diffraction field,and the direction and the amplitude of the shifts is closely related with the topological charge. These results have been demonstrated experimentally in this paper. In addition,the spiral spectral of vortex beams transmitted through the single-slit has also been discussed. It is shown that the spiral spectrum will be broadened due to the limit of the single-slit,and the broadening depends on the topological charge,the beam size,and the width of the single-slit.