Medium-milled rice is increasingly valued for its health benefits and distinctive aroma, which differs from that of white rice because differences in milling degree modify the content of lipids and other aroma precursors. However, its aroma profile remains underexplored. This study aimed to systematically analyze aroma differences among four Simiao rice cultivars after medium milling (8% degree of milling) and to elucidate the chemical basis underlying consumer preference. Odor sensory evaluation identified Xiangzhuxiang as the cultivar with the highest aroma acceptance. Subsequently, gas chromatography–olfactometry–mass spectrometry and odor activity value analysis characterized the volatile profile, identifying 45 volatile compounds across the four cultivars, including 17 key odor-active components. Multivariate statistical analysis pinpointed the discriminating key odor-active compounds responsible for the superior aroma quality of Xiangzhuxiang. The results showed that (E,E)-2,4-decadienal and indole (VIP > 1.0, FDR-adjusted q < 0.05, FC > 1.2, OAV > 1.0, confirmed by GC-O) significantly increased the aroma scores of Xiangzhuxiang; imparted nutty, fatty, and sweet notes; and thus played a decisive role in shaping its characteristic aroma. Moreover, the moderate levels of hexanal and octanal in Xiangzhuxiang facilitated its characteristic aroma expression. These findings provide a basis for developing premium fragrant Simiao rice cultivars optimized for medium milling.