The interference of two vortex beams with equal but opposite topological charges is studied theoretically.The change of the topological charges and the interference properties of vortex beams are explored experimentally.The results show that the vortex beam with the topological changes,whose number is integral time of 0.5,can be easily distinguished by Mach-Zehnder interference method with doveprism while the other fractional order of the vortex beam is more difficult to be distinguished.