To facilitate the application of the extrusion technique in the manufacture of short-fiber- reinforced cement-based building products, the rheological behavior of the fresh cementitious extrudate in an extruder has been studied. In this study, the fresh cementitious extrudate was modeled as a viscoelastic material moving in a three-dimensional extruder channel. The viscosity-related and elasticity- related material parameters were obtained using a homemade rheometer. The governing equations were linearized and solved numerically by the finite-difference method, using the suitable velocity and stress boundary conditions. The velocity profiles of the fresh cementitious extrudates were obtained and discussed. These results were useful in guiding both the die design of an extruder and the mixing proportion design of cementitious composites.