Abstract: To develop the lightweight and high-performance large-aperture silicon carbide (SiC) space primary mirrors, the combination of topology optimization methods and ceramic additive manufacturing techniques provides an effective strategy. The lightweight and thin design method was designed with the back support structure of the silicon carbide space primary mirror, with the maximum stiffness as the design objective and the total mass of the silicon carbide space primary mirror as the constraint. Additionally, this novel method was designed while considering the ceramic manufacturability constraints, based on the Heaviside-function based directional growth topology parameterization (H-DGTP) method. Firstly, the lightweight and thin design method designed a lightweight and thin configuration of the silicon carbide space primary mirror body with ceramic manufacturability, based on the actual requirements of a typical large-diameter silicon carbide space primary mirror. Then, the size optimization method was used to reconstruct and refine the topology-optimized silicon carbide space primary mirror structure. Furthermore, the ceramic sample of the silicon carbide space primary mirror was successfully prepared by the digital light processing (DLP) ceramic additive manufacturing technology, which verified that the designed lightweight and thin configuration of the mirror body meets the manufacturability requirements of ceramic additive manufacturing. Numerical simulation was carried out for the design scheme of the lightweight and thin method. The root mean square (RMS) values of the silicon carbide space primary mirror normal axis along the x, y, and z directions under self-weight load are 3.27 nm, 3.27 nm, and 7.55 nm, respectively. Moreover, the area density of the silicon carbide space primary mirror is 13.21 kg/m². The analysis results show that the optimized large-aperture silicon carbide space primary mirror meets the design requirements of surface accuracy and greatly reduces the weight of the mirror. The results verify the effectiveness of the proposed method for the lightweight and thin design of additive manufacturing silicon carbide space primary mirror.