We propose a new method to detect the orbital angular momentum(OAM) of Bessel vortex beams by an elliptical screen covering the partical azimuth angle. When the diffraction screen is illuminated with a vortex beam, the far-filed diffraction pattern can be used to determine the modulus and sign of topological charges. It was found that the diffraction patterns can best reflect the topological charge information when the angle of initial position is set as 8° and span angle of opaque region of the ellipse aperture is set as 4°. The simulation results show that the number of dark fringes denotes the number of topological charge. The sign of topological charge is determined by the direction of intensity pattern, which flips by 180° for a change in the sign of topological charge. This new method to detect of vortex beam topological charge information is very simple and low-cost.