This paper proposes a dual-channel circularly polarized terahertz metasurface that operates on the principle of co- and cross-polarization multiplexing.By synergistically combining the geometric phase and propagation phase principles,independent phase control over the reflected co-polarized and cross-polarized circularly polarized waves is achieved.The proposed meta-atom comprises a double-layer cross-shaped metal patch and a bottom metal ground plane.Full-phase coverage for both x- and y-polarized linear waves is accomplished by varying the arm lengths of the cross structure.Through an analysis of the decoupling conditions between co- and cross-polarizations,and by concurrently optimizing the arm lengths and rotation angle of the cross,independent phase profiles for the reflected co-polarized and cross-polarized waves are realized.Based on this meta-atom,a terahertz orbital angular momentum (OAM) beam generator is designed.Under normal incidence of a 0.8 THz right-handed circularly polarized (RCP) wave,the metasurface simultaneously generates a left-handed circularly polarized (LCP) wave carrying a +1-order OAM mode and an RCP wave carrying a +2-order OAM mode.The proposed metasurface exhibits promising potential for applications in terahertz communications,radar,and imaging systems.