The linear dispersion relation of Slow Wave Structures(SWSs) driven by annular beam with finite magnetic field was obtained. Numerical analysis was carried out according to the experimental parameters. Based on the PIC simulation results obtained by KARAT, elementary experiment was designed and carried out, from which the terahertz wave with frequency >0.14 THz, pulse duration of 1 ns-2 ns and output power >100 kW was acquired.