Aiming at the problems of rope-twining failure occurred in the process of ring-twining of the knotter hook, virtual knotting method was applied to analyze the influence of rope-lapping point position on the rope-griping plate and inclination angle of the boss on the knotter hook on ring-twining and rope-biting motion, which drew the conclusions that rope-lapping point position deviation was a main factor resulted in rope-twining failure of the knotter hook and decreasing inclination angle of the boss on the knotter hook was beneficial to avoid rope-twining failure of the knotter hook. The critical condition for the rope non-sliding upward along the boss curved surface on the knotter hook was established by force analysis, and inclination angle of the boss of the improved knotter hook was obtained. Based on boundary similarity and B-spline surface modeling method, the boss curved surface of knotter hook was reconstructed under CATIA software and the improved knotter hook model was obtained. Totally 600 knotting tests showed that the knotter hook model with 50° inclination angle of the boss had a better effect of restricting the rope to slide upward along the boss curved surface on the knotter hook, which can effectively prevent the rope-twining failure of the knotter hook. The knotter hook model with 50° inclination angle of the boss may improve the knotting reliability of the knotter, and provide a reference for the improved design of the knotter hook. To the ring-twining of the knotter hook with 60° inclination angle of the boss, rope-lapping point position deviation on the rope-griping plate should be controlled within ±3°. The knotter hook with 50° inclination angle of the boss allowed the rope-lapping point position deviation to range from -4.5° to 3°. They may provide a reference for the position control of rope-lapping point on the rope-griping plate.