Development assurance level is the key technique for civil airplane development process. The deifnition of item development assurance level of civil airplane product was studied. The differences about the allocation principles between SAE ARP 4754a, RTCA DO-178B and DO-254 and relevant reasons were analyzed. In order to solve this issue, the purpose of development assurance, possible solutions and relevant policies were researched. Based on these researches, item development assurance level allocation general principles were suggested. Then, an example was given to show its application practicability.%研制保证等级是民用飞机研制过程的关键技术。研究了民用飞机产品项目研制保证等级定义，解读并分析了SAE ARP 4754A、RTCA DO-178B以及DO-254各标准有关项目研制保证等级的分配要求差异及产生差异的原因。为解决各标准要求差异导致分配结果不一致的问题，在研究研制保证的目的、解决方法以及相关政策要求的基础上，提出关于民用飞机产品项目研制保证等级若干通用分配原则建议，用于指导项目研制保证等级分配的实际应用。并且，通过应用案例表明该分配原则的可行性。
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