Abstract: Objective: Computational fluid dynamics analyses were conducted to determine the factors that influence the in-run phase of ski jumping. The purpose of this study is to determine the factors that influence the speed of taking off, so as to help athletes to optimize their posture and reduce the air resistance in the in-run phase, so that they can achieve higher take-off speeds under the same conditions of start gate, providing targeted theoretical support for training and competition. Methods: Based on the physical data of male ski-jumping athletes, a highly targeted digital twin model was established, then the model was used to do the computational fluid dynamics analysis, so as to provide an optimal posture and angle range. The athletes maintaining a relatively stable action in the in-run stage with the optimal position to obtain a higher starting speed and jumping height under the same conditions. Results: Within a certain range, the lower of distance of the torso from the ground, the higher lift force was obtained by the athletes during the in-run stage. In addition, position with the maximum lift-to-drag ratio does not achieve the maximum in-run and take-off speed. Conclusions: The main reason for the higher take-off speed achieved by adjusting the in-run posture is the reduction in air resistance and the order of magnitude difference in the amount of lift applied to the system compared to the amount of gravity. Therefore, the primary objective of optimizing the athlete's posture during the in-run phase should be to reduce the air resistance as opposed to increasing the air lift. In practice this should be achieved by adjusting the torso and body posture to adjust the in-run posture, optimizing the aerodynamic performance of the multi-body system consisting of the athlete and the equipment during the in-run phase, and achieving drag reduction to achieve better performance.