Sorghum is a crucial food crop, and utilizing heterosis is significant for yield enhancement. To classify heterotic groups in sorghum, 96 inbred lines (48 male sterile lines and 48 restoring lines) were previously analyzed using whole-genome resequencing (WGRS) technology, from which 9691 high-quality SNP markers were obtained. In this study, the materials were divided into two groups—Group I (36 lines; predominantly restoring lines) and Group II (60 lines; mainly male sterile lines)—according to their genetic distances, and 8 lines were selected from each group for incomplete diallel crosses, producing 64 hybrid combinations for analyzing ten agronomic traits and their relationship with heterosis and combining ability. Heterosis analysis revealed that yield-related traits (plant weight, grain yield, and single-spike grain weight) exhibited the strongest heterosis, followed by morphological and developmental traits. The general combining-ability variance exceeded the specific combining-ability variance for traits controlled by additive gene effects. The results demonstrate that WGRS technology effectively classifies heterotic groups in sorghum, providing scientific support for parent selection in hybrid breeding. While combining-ability analysis offers higher predictability for heterosis than molecular genetic distance, genetic distance remains valuable for predicting heterosis.