Abstract: Flax has been one of the most essential oilseed and cash crops in the northern and northwestern hilly regions of China. Flax stems are fiber-abundant and have high nutritional value in their seeds. Mechanical harvesting of flax can rely primarily on segmented picking with combined harvesting at present. However, the entanglement of flax stem during harvesting has emerged as a significant bottleneck, severely impacting harvesting efficiency and industrial development. The power and space layout of a combined harvester are limited in the hilly areas, due to the high cellulose content of flax stems, strong toughness, intertwining capsules, and fruits during maturity. The stems can be easily entangled in the conveyor churn during harvesting. Low mobility cannot fully meet the large-scale production in recent years. This study aims to investigate the influence of the key components of the header in the common grain combine harvester (T₁ model) on the motion attitude of the flax plant. A discrete element flexible model of the flax plant was constructed using MBD-DEM co-simulation technology. A systematic analysis was also made to clarify the tangling mechanism of the header in the common combine harvester. An anti-entanglement plate device was proposed to solve the tangling of the header in order. The key components of the header (T₂ model) were optimized to determine the motion behavior of the flax plant. The anti-entanglement mechanism of the flax header was also clarified after optimization. Finally, a field test was carried out for the verification. The simulation results indicate that there was a greater variation in the average X-axis velocity of the flax plant before 0.6 s, compared with the T₁ model only. Once the flax segments entered into the high-speed movement, the average X-axis velocity minimally changed on the different segments until 0.6 to 0.85 s. The flax segments were turned into a relatively stable movement after 0.85 s. At the same time, the plants accumulated at the spiral blade, accompanied by their rotational motion and the propulsion provided by the spiral blade, leading to the entanglement of the flax stem. Before 0.45 s, minimal variation was observed in the Z-axis velocity of the flax plant segments in the T₁ model. But after that, these velocities tended to change significantly within a narrow range. Specifically, the X-axis velocity of the flax plant segments was accelerated in the T₂ model from 0.64 to 0.77 s. While the flax segments experienced high-speed movement from 0.77 to 1.5 s. An anti-entanglement plate was added to the header to significantly adjust the X-axis velocity. There was a minimal variation in the Z-axis velocity of the flax plant segments in the T₂model before 0.55 s. But after that, these velocities tended to change significantly. Field verification demonstrates that the T₁ model shared a total loss rate of 3.32%, an impurity rate of 3.57%, four instances of winding, and an efficiency of 0.14 hm²/h; The T₂ model presented a total loss rate of 2.29%, an impurity rate of 3.39%, no instances of winding, and an efficiency of 0.23 hm²/h, indicating a 39.13% improvement in the operational efficiency over the T₁ model. The operational performance of the T₂ model fully met the requirement of the flax harvesting. The finding can also provide valuable insights for the design and testing of flax combine harvesters.