The invention discloses a preparation method for porous silicon carbide ceramic with vermiform crystalline grains. The method comprises the following steps: a carbon nanometer tube and SiC of a micrometer scale are taken as raw materials, and rare earth oxide is taken as a sintering additive; under an atmosphere condition of argon, firstly, through the in-situ gas-solid reaction of a gaseous phaseevaporated by SiO powder and the carbon nanometer tube, a block body of which the nanometer SiC is evenly distributed is obtained; then, through high-temperature liquid phase sintering, the porous silicon carbide ceramic with the vermiform crystalline grains can be obtained. The size of the SiC crystalline grain inherits the initial form of the carbon nanometer tube, and therefore, the porous material has relatively high intensity. The preparation technology is simple and easy in operation, a hole size and a porosity can be effectively controlled through portioning and blending raw materialsand changing sintering temperature and heat preservation time. The porous silicon carbide ceramic obtained by the preparation method can be widely applied to fields including high-temperature filtersor catalyst carriers and the like.