To address the challenges of poor amplitude consistency and narrow phase-shift bandwidth in terahertz Reconfigurable Intelligent Surfaces(RIS), a transmission-type coding metasurface is proposed based on diode controlled mirror-symmetric structures, enabling high-efficiency, wideband, and wide-angle Sub-THz beam manipulation. By alternately turning on and off the diodes on the left and right sides of each column control unit, the surface current direction is reversed, thereby realizing 1-bit phase modulation of the incident electromagnetic wave. Through combined CST and Matlab simulations, the unit cell's amplitude and phase responses are investigated as well as the array radiation characteristics. Results indicate that, at the operating frequency of 140 GHz, the unit cell exhibits excellent cross-polarization transmission amplitude consistency, with a cross-polarization transmission coefficient of -2.6 dB and a 180°±10° bandwidth reaching 32%. An 8×1 sub-array designed with this unit cell demonstrates strong polarization conversion capability and array uniformity. When an 8×8 coding array is coupled with a rectangular horn at an optimal focal-to-diameter ratio of 0.64, the metasurface achieves an aperture efficiency of 70% and a beam-scanning range of ±60°. This study provides an effective solution for high performance beam reconfiguration in terahertz communication and imaging systems.