The division of line maintainable parts is one of the important tasks in the maintainability design of civil aircraft. The division of line maintainable parts is the result of a comprehensive balance of economy, maintainability, and reliability, and is the most direct manifestation of customer needs. Reasonable division of line maintainable parts can increase aircraft utilization, reduce maintenance costs, and increase airline profitability. The division of line maintainable parts of domestic civil aircraft is generally based on the experience of similar aircraft types, and lacks a scientific and systematic division method. The division of line maintainable parts is one of the urgent problems in the RMS field in recent years. According to actual needs, this paper puts forward the principle of dividing the line maintainable parts. Based on the preliminary qualitative analysis and quantitative trade-off, comprehensively considering the line replaceable limits, the experience of similar aircraft, economy, reliability and maintainability indicators, this paper proposes a comprehensive trade-off method for the division of line maintainable parts so as to realize the scientific division of line maintainable parts for civil aircraft, and provides support for the reliability and maintainability design analysis of civil aircraft.