Based on the winding process of DC-link capacitor in this paper，the influence of winding tension on the inter-layer pressure and its variation are analyzed. The conclusion that the maximum pressure of inter-layer is directly proportional to the outer diameter of the element and the winding tension stress and is inversely proportional to the diameter of the mandrel is obtained. The limiting requirements of the outer diameter of the circular element on the winding tension and stress are analyzed. The reduction of the winding tension is required when the diameter of the element is increased. The relationship between the winding angular and linear speed is analyzed，and the conclusion that the variation rate of the angular and linear speed is identical is obtained. The variation curve of typical winding speed with time shows that the element winding process contains starting zone，burning zone，accelerating zone，stabilizing zone，decelerating zone and finishing zone. It is proposed that the accelerating zone is the key of the winding process of the element. The calculation method that the additional winding tension can be formed by the acceleration in the accelerating zone is analyzed and the conclusion that acceleration is a time-varying parameter and affects the additional tension in real time is proposed. It is proved through the theoretical analysis and some photos of the research and development process that the joint part of the winding accelerating zone and the winding speed stability zone of the element is the concentrated zone of element breakdown in the durability test，and solving this problem is the key point of DC-link capacitor. It is of great significance for engineers and technicians to understand and solve the winding process problems.