Terahertz (THz) radiation generated by femtosecond laser-pumped photoconductive antenna (PCA) is the most widely used THz wide-frequency source at present. A hemispherical or super-hemispherical silicon lens is usually integrated with a PCA to improve its radiation directivity, beam quality, and radiation efficiency. However, due to the misalignments of the laser focused spot, and between the PCA and the silicon lens, the THz radiation center is not on the rotation symmetrical axis of the silicon lens, resulting in the deviation of THz radiation direction, the deterioration of THz beam quality, and the reduction of radiation efficiency. In this work, a GaAs Schottky detector, mounted on a two-dimensional translation stage was used to obtain the spatial profile of a THz beam radiated from a PCA integrated with a silicon lens. The influence of misalignment between the PCA and the silicon lens on the radiation directivity was clarified. The problem of how to adjust the position of the lens when the radiation of the PCA is offset in the experiment is solved. The effects of misalignment between the PCA and the silicon lens are numerically simulated by using the CST electromagnetic simulation package. The simulation results are consistent with the experiment data.