Significance: With the expansion of deep space exploration endeavors and increasing demand for satellite constellation networking, the global aerospace industry is experiencing a strategic shift from singular payload launches toward a high-cadence and cost-effective transportation paradigm. Consequently, launch vehicle technology has exhibited a discernible trend toward heavy-lift capacity and reusability. To achieve the technical objective of obtaining substantial takeoff thrust, heavy-lift rocket primary engines typically employ a power architecture involving multiple engines operating in parallel. Heavy-lift rockets are poised to assume a pivotal role in forthcoming space transportation missions. As a fundamental component of a rocket launch system, the primary function of the deflector is to direct the controlled diffusion of high-temperature and high-velocity gas jets through a precisely engineered aerodynamic configuration. This mitigates aerodynamic forces exerted on the rocket body and payload resulting from shock wave reflection and attenuates the thermal loading induced by gas backflow. The deflector ensures the structural integrity of the rocket body. Consequently, future heavy-lift rocket launch missions present unprecedented technical challenges for launch site deflectors. These deflectors must achieve large-scale gas evacuation, high-reliability thermal protection, and rapid reusability capabilities in an extreme gas jet environment. The formulation of a deflector design amenable to future heavy-lift rockets necessitates the resolution of several key scientific questions and the circumvention of prevailing technical limitations. Progress: In the field of the flow characteristics of multinozzle gas jets, the multiphysical field coupling process is the main focus. The interaction between the jets and the free flow forms a complex flow structure comprising shear layers, recirculation vortices, and impingement-reversed flows. The pressure ratio of combustion chamber to ambient has a decisive influence on the interaction mode of gas jets. The coupling of the reignition reaction and jet interaction can induce the formation of local high-temperature regions, and the entrainment effect of the vortex structure on high-temperature gas will intensify thermal erosion, which has important guiding significance for the design of thermal protection systems. In the field of the impingement flow of gas jets on inclined plates, the typical flow pattern under the jet-wall interaction is studied. The factors influencing the flow pattern include the impingement height, impingement angle, jet core Mach number, jet underexpansion ratio, and shock system structural parameters. In the field of flame deflectors, the basic configuration is discussed. The core parameters—impingement height, impingement angle, and deflection direction—are investigated, and the performance characteristics of different configurations of flame deflectors are compared. In the field of flame deflector thermal protection technology, two methods, namely active water-cooling technology and passive material thermal protection technology, are discussed. The cooling efficiency of water sprays is influenced by multiple parameters, such as the spray nozzle layout, spray angle, and mass flow rate. To cope with high-frequency and low-cost launch requirements, the rapid post-launch repair of launch facilities is also an important step in the research of thermal protection technology. Conclusions and Prospects: In terms of flow mechanism, the coupling effect of dense nozzle gas-jet should be analyzed, and the laws of the evolution of the jet mixing boundary layers and water spray mixing should be explored. For thermal protection technology, it is necessary to continue developing high-efficiency and low-cost materials for flame deflector thermal protection to improve the reusability and maintainability of diversion facilities.