Sulfur-containing polymers have been widely studied because of their high refractivity and low dispersion, but the efficient synthetic approach of them is quite limited. In this work, we use the abundantly existed elemental sulfur as monomer to prepare polythioamide directly and efficiently through a facile multicomponent polymerization (MCP) of aromatic diynes, sulfur, and aliphatic diamines. This MCP can proceed smoothly in a catalyst-free manner with high atom utilization to afford polythioamide with well-defined structure, high molecular weight, and high yield. It demonstrates a convenient approach to convert elemental sulfur into functional polythioamide. Fluorescence is observed from the polythioamide, despite the absence of typical fluorophores, owing to the "heterodox clusters" composed of a large number of lone-pair-containing electron-rich heteroatoms. The emission maxima and efficiencies of the polymers depend on the formation of molecular aggregates through intrachain and intermolecular interactions such as hydrogen bonding and n -> pi* interaction between thioamides. This polymerization is anticipated to accelerate the development of efficient and economic MCPs toward functional polymer materials.