Silicon nitride-based ceramics are considered as a kind of promising materials for structural and functional integration due to their robust structure, extreme environmental resistance and electromagnetically transparency. It is still challenging to prepare silison nitride-based ceramics with homogeneous and controllable microstructure because of their low self-diffusion coefficient and difficulty in sintering. Here, we developed a gelcasting-SHS process by combining gelcasting forming and self-propagating high temperature synthesis (SHS) for the preparation of porous Si3N4-based ceramics. By regulating the composition of starting materials, solid content in the initial slurry, binder removal process and SHS process, porous Si3N4-based ceramics with high porosity, high strength, low dielectric constant and dielectric loss tangents were synthesized. At the same time, the structure of porous Si3N4-based ceramics has been systematically investigated, including grain aspect ratio and pore structure, etc. It offered a new perspective to obtain porous ceramics with high porosity and high performance easily and quickly.