Abstract: A dual-band microstrip antenna operating in the terahertz band is proposed. Two rectangular patches are loaded at 45° and 135° on the antenna's radiating patch to increase the radiation area and the impedance bandwidth at the high frequency resonance point. By introducing a defected ground structure(DGS), the current path of the antenna at the ground plate is changed and coupled with the radiation patch so as to realize dual frequency characteristics. In order to increase the gain of the antenna, several parasitic rectangular patches are loaded on the edge of the radiating patch. To further improve the antenna gain, the thickness of the substrate at the parasitic patch is increased, so that the antenna can simultaneously operate well at two bands, namely 520 GHz (508-532 GHz) and 680 GHz (581-766 GHz). The corresponding maximum gains are 3.54 dB and 4.11 dB respectively. One of the relative bandwidth at high frequency reached 27.5%. The dual-band antenna has the characteristics of simple structure and stable performance, and it has the application value for terahertz communications and wireless transmission systems.