Abstract: The design and development process of YF-77， a 50-ton LOX/LH₂ rocket engine for Long March 5 launch vehicle is introduced systematically in this paper. Firstly， by analysing the characteristics of LOX/LH₂ rocket engine and the development status of LOX/LH₂ rocket engine at home and abroad， the technical route of the new generation launch vehicle and the development background of the 50-ton LOX/LH₂ rocket engine are described. Then， the overall technical scheme and characteristics of the 50-ton LOX/LH₂ rocket engine are analysed and summarized， and on this basis， the technical specifications of the main components of the engine are analysed. Then， the test run of the engine， reliability verification and troubleshooting of the engine are analysed. Finally， the development and technical characteristics of the 50-ton LOX/LH₂ rocket engine are summarized， and the development of LOX/LH₂ rocket engine and LOX/LNG engine in China is prospected.

Key words: Liquid rocket engine;Launch vehicle;LOX/LH₂ rocket engine;Overall plan;Engine test run

摘要： 系统性地回顾了长征五号运载火箭芯一级50t级氢氧火箭发动机YF-77的设计与研制历程。通过分析氢氧发动机的特点以及国内外氢氧发动机的发展现状，阐述了国内新一代运载火箭研发的技术路线和50t级氢氧火箭发动机的研制背景；对50t级氢氧火箭发动机的总体技术方案及其特点进行了分析与总结，并在此基础上对发动机主要组件的技术方案及其特点开展分析；对发动机热试车情况、可靠性验证情况和故障排除情况进行了分析；对50t级氢氧火箭发动机的研制情况、技术特点进行了总结，并对国内氢氧发动机和液氧/甲烷发动机的发展进行了展望。

关键词: 液体火箭发动机;运载火箭;氢氧发动机;总体方案;发动机试验