The continuity, momentum and energy equations are employed to describe the fiber compounding process of a twin-screw extruder. The coupled continuity, momentum and energy equations are numerically solved with the help of an approach of computational fluid dynamics to predict the three-dimensional melt flow passing through the investigated twin-screw extruder elements. Fiber movement is traced according to the calculated flow field, where the time history of shear stress and strain rate are also predicted. The dispersion and distribution characteristics of fiber is then assessed by means of the residence time distribution along with the time-integrated shear stress and strain as well as the mixing indices. The behavior of fiber orientation in a compounding process is then predicted by the equation of orientation tensor. Six different twin screws are employed in modeling the extrusion process of fiber compound, where the barrel length is 175 mm accompanied with barrel radius 25.6 mm and axis-to-axis distance 21.1 mm. An isothermal extrusion process at 473 K is simulated under the flow rate of 10 kg/hr and screw speed of 300 rpm. Numerical prediction shows that several twin-screw configurations deliver high residence time to reflect a favorable distributive mixing feature. High mean shear stress of the rest twin-screw configurations further depicts better dispersive characteristics in mixing. The comparison of strain-rate-type identifier suggests some twin-screw configurations show an unfavorable distributive mixing nature among the investigated twin screws, whereas the difference in the Manas-Zloczower mixing index discloses an improved mixing behavior for the other twin-screw configurations. The last twin-screw configuration is predicted to have the best mixing performance among the studied six twin screws, where its fiber orientation also gives a more concentrated distribution. The degree of fiber orientation for the six twin screws is approximately 35%.