With phenolic resin as carbon source, ethylene glycol as solvent and pore-forming agent, and silicon monoxide as pore-forming agent and silicon source, a kind of light hierarchical porous silicon carbide (SiC) ceramics with adjustable pores was prepared by gelcasting, carbonization and carbothermal reduction. With the addition of silicon monoxide in the green body from 13 to 49%, the porosities increased from 66 to 89%, the densities and thermal conductivity are as low as 0.36 g·cm⁻³ and 0.29 W·m⁻¹·K⁻¹. The macropores are mainly determined by the addition of silica particle size, which increases from 9.2 to 39.5%, while the micropores and mesopores, ranging from 56.8 to 49.5%, are mainly determined by the pyrolysis of resin carbon source. When the porosity of porous SiC is 75%, the compressive strength of 7.83 MPa can be reached. The prepared porous SiC ceramics possessed light, good thermal insulation and other properties, which can be further improved by changing the shape and size of the added SiO particles. In addition, different from using polycarbosilane as preceramic polymer, the porous SiC ceramics with complex shape and uniform microstructure can be prepared via gelcasting, which will reduce the production costs and broaden its application.