Abstract: Terahertz (THz) pulses after spatiotemporal shaping have been widely applied to THz spectroscopy and imaging. We simulate the shaping effect of rectangular and circular apertures by employing the three-dimensional (3D) finite-difference-time-domain (FDTD) method. The simulation results show that we can realize effective shaping and filtering of THz pulses using rectangular and circular conductive apertures of finite thickness. When the long side of the rectangular aperture is perpendicular to the polarization direction of the incident wave, the rectangular aperture has a good influence on the shaping and filtering of THz pulses. However, when the long side of the rectangular aperture is parallel to the polarization direction of the incident wave, it almost has no obvious effect on the shaping and filtering of THz pulses. The circular aperture has more obvious effect on shaping of THz pulses than the rectangular aperture. Moreover, these simulation results can be interpreted qualitatively by the theory of planar waveguides.