Abstract: The effects of twin screw extruder (TSE) and model screw device (MSD) on fiber morphology and pulping properties of pulp were investigated under the same APMP pulping process.The result showed that the low contents of fibril bundle and long fibers could be obtained under extrusion degree at the same pulping process. The TSE could result in a fiber bundle content of 1.78% in the Canada freeness of 250 mL. Compared with MSD extrusion, the extrusion decreased by 76.67%. In addition, the bursting strength and tensile strength of the pulp from TSE were higher than that of the untreated poplar and MSD treated poplar. However, the tearing strength of the pulp from TSE was lower than that of the pulp of untreated and MSD treated poplar because of the low content of long fiber. The brightness of pulp from TSE reached 65.48% in the Canada freeness of 250 mL, increased by 9.14% and 12.94% compared with MSD extrusion and the untreated poplar, respectively. The yield of the pulp was 84.54%, which was lower than the pulp yield of the MSD treated (87.20%) and the untreated poplar (87.00%), that because TSE dissolved more poplar compositions during the pulping process. Mean while, the wastewater pollution index was higher.