Abstract: The terahertz (THz) radiation properties of photoconductive antenna (PCA) were studied. The radiation characteristics of photoconductive antenna were simulated using FDTD; the results calculated were displayed on a computer in pseudo-color graphical. Using electric dipole antenna model and taking 0.1THz as an example, equatorial plane and the meridian plane of the antenna pattern were obtained, the antenna radiation resistance is 790 ohm, and directivity factor is 1.5. The results show that photoconductive antenna can be calculated with dipole antenna theory. Radiation resistance is increased by increasing the electrical length, and the power of terahertz radiation is increased as well.