A novel slit with angular transmittance is proposed and the interference patterns of a vortex beam transformed through the angular slit are investigated theoretically and experimentally with the angular slit by CCD. The method is the observation of the interference pattern. The theoretical results are simulated based on the intensity expression in the far field, which are in consistent with the experimental results .The influence of the slit number and topological charge on the interference pattern are investigated. It is shown that, the interference pattern depends on the number of the angular slits and the topological charge of the vortex beam. It results from the change of the vortex beam phase. The result may have potential application in measuring the topological charge of a vortex beam.