The structural and electronic properties of sulfur-doped armchair stanene nanoribbons (ASnNRs) have been investigated using Density Functional Theory (DFT). The diverse structural and electronic characteristics induced by the substitution of sulfur atoms were comprehensively analyzed through first-principles calculations, including formation energy, optimized structural parameters, projected density of states (PDOS), and spatial charge density distribution. Various doping configurations were considered by replacing Sn atoms with S at different concentrations and atomic positions, resulting in characteristic doping types such as single-atom doping (top-1S, valley-1S), two-atom doping (ortho, meta, para), and full 1:1 substitution with a 6Sn–6S structure. The results reveal significant changes in the bandgap, increasing slightly from 0.26eV in the pristine state to approximately 0.34eV in the meta configuration, moderately decreasing to 0.15eV in the 100% substitution case, and sharply decreasing in the other configurations. Moreover, most sulfur-doped configurations exhibit non-magnetic behavior similar to pristine ASnNRs, while strong magnetism emerges only in the fully substituted 100% case. These findings demonstrate that sulfur doping can fundamentally modify the electronic and magnetic properties of the material, highlighting its potential application in future spintronic devices.