To achieve relatively high frame rates with relatively low costs, a Tshaped terahertz imaging system with beamscanning function is presented. The system employs two orthogonally oriented copolarized scanning fanbeam antennas arranged in a Tshaped configuration. Both transmitting and receiving antennas consist of a pyramid horn feed, a fixed elliptical mainreflector to generate thin fan beam, and a rotating subreflector to realize beam scanning function, all of which are embedded between two parallel metal plates. In this paper, specific design details of such a system were discussed, especially for the systematic method proposed to design a fanbeam scanning antenna with high performance. In addition, some experimental imaging results were shown, which demonstrated the capability of the system.