In order to manipulate terahertz wave flexibly, a terahertz tunable coding metasurface unit cell structure is designed based on the Pancharatnam-Berry phase principle and the use of graphene material. It consists of a double-open θ-shaped metal structure on the top layer, a polyimide substrate embedded in a double-layer graphene structure and a metal layer, and its reflection amplitude can be dynamically tuned by modulating the Fermi energy of the bilayer graphene structure. Based on its amplitude tunable characteristic, a coding sequence with rotational phase gradient characteristic is designed to generate an amplitude tunable vortex beam. Combined with the Fourier convolution theory, a coding metasurface capable of emitting a double vortex beam is designed ulteriorly, and the maneuverability of vortex beam numbers and scattering angles is greatly improved in this way. The device designed has potential applications in terahertz high-speed communication system.