Close planting of dwarf varieties is currently the main cultivation direction for pear trees, and the screening of excellent dwarf varieties is an important goal for breeders. In this study, the dwarfing pear variety \'601D\' and its vigorous mutant \'601T\' were used to show their biological characteristics and further explore the dwarfing mechanism in \'601D\'. The biological characteristics showed that \'601D\' had a shorter internode length, a shorter and more compact tree body, thicker and broader leaves, lower stomata density, larger stomata size (dimension), and higher photosynthetic capacity. The biological characteristics of \'601T\' showed notable contrasts. The results of endogenous hormone tests indicated that the contents of abscisic acid (ABA), ABA-glucosyl ester, and GA4 were higher in \'601D\', but the trans-zeatin content was lower. By transcriptomic analysis, significant differences were found in the biosynthetic and metabolic pathways of ABA. Related transcription factors such as bHLH, WRKY, and homeobox also participated in the regulation of plant dwarfing. We therefore examined three hormones with obvious differences with \'601T\', and found that only ABA could induce \'601T\' to return to a dwarfing plant phenotype. Therefore, we conclude that the dwarfing of \'601D\' is caused by an excessive accumulation of ABA. This study provides a new theoretical basis for breeding dwarf varieties.