AbstractA twin‐screw extruder with an ultra‐large length‐to‐diameter (L/D) ratio of 136 was developed and applied in the gel‐spinning process of ultra‐high molecular weight polyethylene (UHMWPE). UHMWPE gel fibers with concentrations of 6–18 wt% were produced at barrel temperatures of 150–180°C and screw speeds of 10–40 rpm. The residence time of the UHMWPE gel solution in the extruder increased with the increase of solution concentration and barrel temperature and decreased with the increase of screw speed. The tensile properties and crystallinity of the UHMWPE gel fibers decreased with the increase of solution concentration. Due to the great shear effect of the ultra‐large L/D ratio, the barrel temperature and screw speed could be lower to optimize the structure and tensile properties of UHMWPE fibers. Compared to the extruder with the L/D ratio of 36, the tensile strength, modulus, and elongation at break of the gel fibers prepared by the extruder with the L/D ratio of 136 were increased by 148.8%, 117.6%, and 54.2%, respectively. The crystallinity of the gel fibers was increased by 50.6%. The fiber had a dense and smooth surface with oriented fibrils, which indicates the great ability of the ultra‐large L/D ratio for disentanglement of molecular chains.