Propagation of a femtosecond THz pulse in random scattering media is described using Monte-Carlo simulation. We study the effects of the radius of scattering spheres and the depth of scattering media, in relation to the parameters of scatt ering coefficient and anisotropic factor by Mie theory. The results show that wh en Mie theory holds, the smaller the spheres, the more the THz pulse is scattere d. The scattering effect expands in the width of pulse in temporal domain and re duces the imaging resolution of THz pulse in random scattering media.