The photoconductive antenna and array are one of the important methods to generate terahertz wave. Gallium arsenide is the common substrate material of photoconductive antenna, and its refractive index is relatively high. The coupling degree of terahertz wave at the substrate-air interface is low, which affects the radiation efficiency of the photoconductive antenna. It is an important way to improve the radiation efficiency of the photoconductive antenna to improve the coupling of terahertz wave on the two medium interfaces. In this paper, the influence of the silicon lens on the radiation of the photoconductive antenna is studied. Terahertz radiation of 2 × 2 photoconductive antenna array is researched by ray tracing analysis. The influence of silicon lens on terahertz radiation efficiency of the photoconductive antenna array is analyzed. The results show that the silicon lens can improve the coupling between the substrate and air, and enhance the radiation efficiency of the gallium arsenide photoconductive antenna array. When the radius of the silicon lens is 4mm, THz radiation intensity which is received by the first off-axis parabolic mirror in the terahertz time domain spectrum system of transmission mode is the highest. This lays a theoretical basis for improving the radiation efficiency of the photoconductive antenna array.