Line Replaceable Unit (LRU) is treated as a unit for fast fault detection and real-time replacement, which can effectively avoid the phenomenon of aircraft on ground (AOG) during operation, and improve maintenance efficiency. Under the condition of meeting the continuous airworthiness requirements, the safety and reliability of civil aircraft can be ensured. To reasonably and effectively derive LRU division of civil aircraft, Based on the comprehensive consideration of many factors in the stage of design and operation process of civil aircraft, this paper proposes a LRU division method, namely two-step iterative analytical hierarchy process (TSI-AHP, short for), on the premise of considering the influence of various factors in the design stage and operation process of civil aircraft. Firstly, the influence of relevant factors in the design and operation stages on LRU division of civil aircraft is investigated. Secondly, the influence of various factors are comprehensive considered, and the lowest structures of product decomposed by their function are regarded as the study objects, and the TSI-AHP is applied to implement LRU division of civil aircraft. Finally, the landing gear system of ARJ21-700 aircraft is treated as an example to realize the LRU division using the method proposed. The analytical shows that the proposed TSI-AHP can effectively accomplish the LRU division for the landing gear system of ARJ21-700 aircraft, and the effectiveness and applicability of the method for LRU division are verified compared with the data in engineering practice. The efforts of this paper provide an effective guidance for LRU division of domestic civil aircraft.