Out-of-Autoclave (OoA) curing technology, eliminating the need for autoclaves and using vacuum pressure to cure prepregs, has gained attention in aerospace as an advanced composite manufacturing process. This approach leads to substantial reductions in production costs and time. This paper mainly investigates the vacuum bag-only(VBO) technology of Out-of-Autoclave (OoA) prepreg for the sandwich fairing structure of Hybrid – Electric Vertical Takeoff and Landing (H-eVTOL) aircraft. It comprehensively examines the latest research progress in OoA prepreg forming technology both domestically and internationally, covering material systems, process methods and application scopes. Combined with the special requirements of H-eVTOL aircraft for sandwich fairing structures, such as high strength, low weight, and good aerodynamic performance, the paper explores how to achieve low-porosity molding effects. It takes several key measures, like designing material curing process parameters, improving the pre-compaction packaging system, and creating a three -dimensional air channel in the vacuum bag. The sandwich fairing structure with low porosity is effectively prepared, and its mechanical properties reach the level of autoclave curing, providing technical support for the high – performance and lightweight design of H – eVTOL aircraft.