The processing difficulties of UHMWPE caused by the wall slip can be solved effectively by the eccentric rotor extruder, which make the melt conveyed in positive displacement. To reveal the melt flow characteristics of UHMWPE in the conveying section of the eccentric rotor extruder, the model parameters of wall slip were determined by the combination of experiment and numerical simulation, and the flow field of UHMWPE melt was numerically simulated by ANSYS Polyflow. The results show that the UHMWPE melt in the cavity formed by the meshing of the rotor and the stator can be conveyed in positive displacement, and the change in the cross-sectional size of the cavity leads to the elongation flow field in the melt. When the meshing gap exists, the positive pressure and negative pressure formed around every inlet and outlet respectively, will lead to the counterflow and leakage of the melt in the cavity and make the average flow rate at the outlet of the cavity lower than the theoretical flow rate. When UHMWPE is processed by the eccentric rotor extruder, the instantaneous flow rate and average flow rate of the melt at the outlet of the cavity are proportional to the rotor rotation speed, while the pulsation rate of the flow rate remains unchanged. Reducing the meshing gap between the rotor and the stator increases the average flow rate of the melt at the outlet of the cavity and decreases the pulsation rate of the flow rate, which enhances the positive displacement conveying of the melt in the eccentric rotor extruder.