The invention relates to a suspended microstrip circuit-based terahertz duplexer bridging F-G frequency bands. The terahertz duplexer is a cuboid cavity structure and comprises an upper cavity (8) anda lower cavity (7), wherein the upper cavity (8) is formed above the lower cavity (7), a surface of the upper cavity (8) is closely attached onto and fixed with a surface of the lower cavity (7), a suspended microstrip circuit (9), a standard waveguide input passage (24) and a first standard waveguide output passage (23) are arranged at an attachment position, the standard waveguide input passage(24) and the first standard waveguide output passage (23) are arranged at two ends of the suspended microstrip circuit (9) to form a Pi-shaped structure, and a second standard waveguide output passage (25) is arranged between standard waveguide input passage (24) and the first standard waveguide output passage (23).