As a core functional component of aircraft, the assembly process of aircraft major components faces the industry challenge of uncontrollable costs and significant fluctuations in efficiency and quality due to discrete processes. This study innovatively proposes a digital production line system framework based on essential cost control. By establishing a multi-factor dynamic collaborative optimization algorithm, it systematically quantifies the cost elasticity coefficients of five core influencing factors: assembly mode, drilling process, energy system, production monitoring, and logistics transfer, achieving precise dynamic mapping between assembly parameters and cost elements. The core breakthrough of this Framework lies in: constructing a dynamic weighting system including five key factors, and through the real-time iterative update of elasticity coefficients, achieving the optimal allocation of process resources; designing a convergence guarantee mechanism based on stability theory to ensure the reliability of the multi-objective optimization process; developing a three-dimensional evaluation system of efficiency, quality, and cost to accurately quantify the comprehensive benefits of process improvement. In the engineering verification of a certain model of aircraft door production line, the innovative digital production line framework for aircraft door assembly significantly reduced the assembly cost per unit by 61.2%, shortened the production cycle time by 34.7%, and increased the CPK of key features to 1.67. The innovative digital production line Framework and key technologies for Civil Aircraft Major Components assembly line based on essential cost control proposed in this study not only solve the cost control problems of traditional assembly modes but also provide theoretical guidance and practical paradigms for the digital transformation of the aviation manufacturing industry.