This paper focuses on the research of precision manufacturing technology for large-sized complex configuration I-beams using domestic materials, with a specific emphasis on carbon fiber-reinforced resin matrix composites applied in the vertical tail beams of a certain aircraft type. Due to long-term import dependence in this field, domestic substitution has become crucial. The study analyzes the unique structural form of the large-sized variable-thickness complex-shaped I-beam and elaborates on the manufacturing difficulties of domestic vertical tail beams, including the adaptability of domestic T800 prepreg in automatic placement, quality control of hot diaphragm pre-forms, and post-forming part quality control. Key manufacturing technologies, such as optimizing the automatic placement adaptability and accuracy control of domestic T800 prepreg, exploring the hot diaphragm pre-forming process, and studying the forming process, are comprehensively investigated. The research results provide valuable references for promoting the localization of large-sized composite parts manufacturing and ensuring the stable supply of aircraft components.