Three-dimensional flow field of triangle arrayed triple-screw extruder (TTSE) in different feed rates, screw speeds and screw configurations were simulated by POLYFLOW. Polypropylene processing by TTSE was tested to validate the numerical simulation. The reliability of simulation was tested directly and indirectly by comparing the axial pressure difference and residence time distribution (RTD) separately. The results show that the axial pressure differences from the simulations and experiments were in high agreement. The simulated and experimental RTD curves show the same trend, and so are the simulated and experimental average residence times. These results prove the reliability of simulation and its guidance to the experiment. POLYM. ENG. SCI., 55:156-162, 2015. (c) 2014 Society of Plastics Engineers