The model and numerical simulation of three-dimensional non-isothermal for sol-gel reaction process of preparing PP/TiO₂ nanocomposites between mixing and reaction process in twin screw extruder were established by POLYFLOW software with the finite element method. The effects of screw speed, screw pitch and precursor concentration on the preparation of PP/TiO₂ nanocomposites reaction process about mixing efficiency and reaction rate were analyzed. The results showed that the increasing pitch which enhanced the temperature of polymer and improved mixing efficiency in twin screw extruder contributes to the reaction process. The increasing screw speed and precursor concentration were not conducive to the reaction, because of the drop of the fractional conversion.