In the investigation,the flow field of a vane unit in the vane extruder on the basis of a volume-extension- al field is numerically simulated by means of the CFD software ANSYS POLYFLOW,and the orientation probability of the fiber of the vane unit in all directions is calculated by substituting the velocity gradient tensor of the flow field into a fiber orientation distribution function.The direction of the maximum value of the orientation distribution func- tion is considered to be the main orientation of the fiber.Then,Matlab is adopted to visualize the orientation distri- bution of the fiber on different profiles along the circumference.The results show that the orientation of the fiber at the entrance of the vane unit aligns to the axial direction，which is the extrusion direction,and the orientation of the fiber far away from the entrance of the vane unit is mainly along the direction which has a certain angle with the cir- cumferential direction and the axial direction.By comparing the fiber orientation distribution with the dispersion in- dex distribution,it is found that the extensional field is more conducive to the fiber orientation than the shear flow field.Finally,the numerical results are verified by the experimental results,finding that they accord well with each other.