In order to get a high flowrate gas-gas injector and its design methodology,the combustion flow field of a typical shear-coaxial injector was analyzed firstly.The dimensional analysis was applied in the phenomenon of gas-gas combustion,and design parameter optimization and a structure improvement were also carried out.A high flowrate single-element injector with high H2/O2 momentum ratio and tapered O2 post tip was obtained and validated by both numerical and experimental studies.This high flowrate injector has simple construction and it can effectively enhance the mixing,decrease the combustion completion length and also has a benign heat environment.Furthermore,based on the study of the single-element injector,numerical optimization and validation experiments were conducted successively on a multi-element injector equipped with high flowrate injection elements.The multi-element injector with the high flowrate elements started up and shut down smoothly,and operated steadily without any stability aids.In the combustor designed with nominal parameters,this injection element can obtain high combustion efficiency with a flowrate of 3.7 times that of SSME main injector element and shows a benign chamber wall heat compatibility.This injector design and the design methodology can become a reference for the design of other types of injectors for liquid rocket engines. In order to get a high flowrate gas-gas injector and its design methodology, the combustion flow field of a typical shear-coaxial injector was analyzed first. The dimensional analysis was applied in the phenomenon of gas-gas combustion, and design parameter optimization and a structure improvement were also carried out. A high flowrate single-element injector with high H2 / O2 momentum ratio and tapered O2 post tip was obtained and validated by both numerical and experimental studies. This high flowrate injector has simple construction and it can effectively the mixing, decrease the combustion completion length and also a benign heat environment. Furthermore, based on the study of the single-element injector, numerical optimization and validation experiments were conducted successively on a multi-element injector equipped with high flowrate injection elements. The multi-element injector with the high flowrate elements started up and shut down smoothly, and operated steadily without an y stability aids. the combustor designed with nominal parameters, this injection element can obtain high combustion efficiency with a flowrate of 3.7 times that of SSME main injector element and shows a benign chamber wall heat compatibility. This injector design and the design methodology can become a reference for the design of other types of injectors for liquid rocket engines.