Based on the square ring monopole antenna element, an ultra wideband circularly polarized microstrip array antenna in terahertz band was designed. By changing the structure of the ring antenna element, the current on the antenna surface could flow asymmetrically, and the circularly polarized wave radiation could be realized by changing the aspect ratio of the current using triangular perturbation. Using 2×4 antenna array not only increased the gain of the antenna, but also optimized the directional characteristics of the antenna. The simulation results show that the antenna array operates at 193.86~391.02GHz, the relative bandwidth is 67.42%, and the maximum gain can reach 15dBi. It has a good application prospect in terahertz communication.