Abstract: The key parameters of processing temperature, reaction time and screw speed for poly(pphenylenebenzoxisoxazole)(PBO) were investigated by orthogonal analysis methods. The processing temperature is the most important, then is the reaction time, and the screw rotation speed is the least in this extruding polymeration process. The post-polymerization kinetics was studied. The polycondensation is controlled by diffusion rate and the kinetics is accorded with the irreversible reaction of the second order. When the extrude temperature heats up from 160 ℃ to 190 ℃, the rate constants of reaction increase by 4 folds. The activation energy is 84.4 kJ/mol.