After comparing wide-band antenna and narrow-band antenna, a dual-frequency Terahertz antenna for wireless communication was designed. It consists of two dipole antennas which are located on two different layers and arranged vertically to avoid connection and interaction. The two dipoles both have THz chokes to improve performance, and different sizes to operate in two different frequencies. The upper dipole uses metal probe to connect the LT-GaAs substrate through the hole of substrate and shares the same photomixer with the lower dipole. The photomixer can be lighted by the same light for pumping, while the two dipoles can be controlled by different circuit for bias. So they can work at different frequencies and in vertical direction of polarizations. They can be adjused for the air’s low-loss frequencies by changing the size. The dual-frequency antenna has higher performance because of the two dipole antennas. At the air’s low-loss frequencies of 0.21 THz, 0.35 THz, 0.41 THz, 0.68 THz, 0.85 THz and 0.93 THz, it has total efficiencies of 14.9%, 28.4%, 33.9%, 28.4% and 216% respectively, and max realized gains of 2.99 dB, 10.6 dB, 11.8 dB, 18.4dB, 18.2 dB and 18.3 dB respectively.