Abstract: Thermoelectric (TE) technology, a solid-state energy conversion technique enabling direct conversion between thermal and electrical energy, holds significant potential for applications such as waste heat recovery and localized cooling. However, the complexity, high cost, and limitations in fabricating intricate geometries associated with conventional manufacturing processes have severely constrained the performance optimization and large-scale application of TE devices. In recent years, additive manufacturing technologies, particularly direct ink writing (DIW) and extrusion-based 3D printing, have opened new avenues for preparing TE materials and designing integrated, customized devices. This review focuses on the application of DIW 3D printing in the field of TE materials. It introduces the core principles of the technology, systematically reviews key process parameters and the performance of printed TE material systems, and analyzes advanced strategies for optimizing TE performance through material composition engineering, microstructural tailoring (e.g., porous, gradient, and lattice structures), and geometric design. Furthermore, this review discusses key challenges in the field, including the rheological design of functional inks, structural fidelity and performance degradation during printing and post-processing, interface contact optimization, and anisotropy. Finally, future directions are envisioned, such as machine learning-assisted design, multi-material and multifunctional integration, in situ characterization, and industrial-scale applications.