We demonstrate a new method to detect the vortex beams carrying orbital angular momentum (OAM) by a sectorial screen. When the sectorial screen is illuminated with vortex beams, the far-field diffraction pattern can be used to define the modulus and sign of topological charges. The number of the petals denotes the number of topological charge. The direction of intensity pattern flip by 180° for a change in the sign of topological charge. The experimental results agree well with the simulated results.