The choice of seismic sources is an important issue in numerical simulation. To demonstrate the importance of the seismic source and investigate the wavefields of different seismic sources in a poroelastic medium, we have developed representations of the seismic sources: the force-density source and moment-density source. In the numerical simulation, we use the staggered-grid finite-difference method to discretize the spatial and temporal derivatives. We compare the numerical results of different spatial functions of a seismic source including the delta function and the Gaussian function, and we find that the numerical dispersion can be suppressed by the Gaussian function compared to the delta function. We compare and evaluate the numerical results for the explosion source, torque source, and force-density source for a 3D homogeneous poroelastic model, which demonstrates that the different seismic sources generate completely different wavefields. In addition, the three seismic sources are used to generate the response of a 3D-layered poroelastic model to investigate the reflected waves at the interface. Our numerical results indicate that the fast P-wave, the slow P-wave, and the S-wave give rise to each other at an interface.