Photo-Conductive Antenna(PCA) is a commonly used terahertz transmitting device. How to improve the radiation efficiency of PCA has become the research focus of domestic and foreign researchers. In this paper, the radiation efficiency of the PCA is studied by using the Finite Difference Time Domain(FDTD) method. The columnar structure is added to the surface of the photosensitive layer, so that more light is captured in the photosensitive layer. The simulation results show that the structure can significantly enhance the radiation efficiency. By comparing the enhancement effects of materials and columnar shapes, the results show that the enhancement effects of the PCA of silver material, gold material, and gallium arsenide material sequentially decrease in the same columnar structure; in the same material, the enhancement effects of the PCA with the regular hexagonal prism structure, the cylindrical structure, and the regular quadrangular prism structure decrease sequentially. Through the optimal combination of materials and structures, the highest and the lowest enhancement efficiencies are respectively 1 100% and 150% that of the traditional PCA.