Investigation on 3D printing of silica ceramic cores is crucial to the development of aviation level in China, but the related problems are high-temperature softening and structural anisotropy. Silica ceramic cores were fabricated by DLP light curing 3D printing technology using fused silica powder as a raw material and mullite powder as a modifier. The results show that the ceramic cores have a layer-packed anisotropic structure. The addition of a small amount of mullite powder promotes the sintering densification of ceramic powder and diffusion binding between printing layers. As a result, the structural anisotropy of ceramic cores is relieved, and the flexural strength is enhanced and tended to isotropy. For ceramic cores with 3% mullite powder, the high-temperature flexural strengths in horizontal and vertical printing are up to 18.5 MPa and 16.3 MPa, respectively, which can satisfy the demands for hollow blade casting.