Diamond nanothreads are one-dimensional crystalline nanomaterials formed by the polymerization of organic molecules under high pressure. Their sp³-hybridized carbon framework endows them with exceptional mechanical, thermal, and electrical properties. This paper systematically reviews the progress in structural prediction, synthesis strategies, and property studies of this material. Theoretical investigations have demonstrated that diamond nanothreads possess wide band gaps, high carrier mobility, and excellent mechanical performance, and that their electronic structure can be effectively tuned through heteroatom doping, defect introduction, and lattice strain. Regarding the synthesis, a variety of ordered crystalline nanothreads have been successfully prepared via high-pressure solid-state reactions using precursors such as benzene, fluorobenzene, pyridazine, s-triazine, and cubane. Through rational precursor molecular design, cocrystal engineering, and regulation of reaction conditions, functionalization and heteroatom doping synthesis have been realized. In recent years, the successful preparation of polymer single crystals with sizes up to hundreds of micrometers using 1-naphthoic acid as the precursor has enabled, for the first time, the direct measurement of anisotropic thermal conductivity. This paper also provides an outlook on future research directions concerning precise structural control, multifunctionalization, and reduced-pressure synthesis.