The invention discloses a preparation method of a silicon carbide porous material. The preparation method includes the steps of: 1) treating main materials, including a SiC particle material and a B4C particle material, to form a slurry finish product, wherein the B4C particle material serves as a sintering aid, the particle size of the SiC particle material is not more than 0.8 [mu]m and the size of the B4C particle material is 3.2 [mu]m; 2) adding auxiliary materials to the slurry finish product to prepare a pre-casting slurry material with stirring during addition, wherein the auxiliary materials include acrylamide, methylene bisacrylamide and ammonium polyacrylate; 3) die casting: adding ammonium persulfate to the pre-casting slurry material with uniform stirring, and performing die casting and demoulding the casted blank body; and 4) dewatering and degreasing the blank body and sintering the blank body. In the technical scheme, the SiC particle material being smaller in particle size serves as a main gel material while the B4C particle material being larger in particle size serves as the sintering aid and a framework material, thus preparing high-quality silicon carbide gel.