Introduction: Pitaya ( Hylocereus spp.), a rapidly expanding tropical fruit crop, faces a critical industry challenge: high yields often come at the expense of sweetness, limiting consumer appeal and market value. This study tests the hypothesis that cultivars with contrasting sugar phenotypes exhibit distinct profiles of sucrose-metabolizing enzyme activities, and that the balance between sucrose synthase (SS) cleavage and synthesis directions determines final sugar accumulation and spatial distribution patterns. Methods: We compared four phenotypically diverse cultivars selected based on preliminary field screening of three key traits: flesh color (white vs. pigmented), average fruit weight (small, medium, large), and soluble solids content (low, medium, high)—'Jindu No.1', 'White Crystal', 'Bicolor Fruit', and 'Bai Yulong'—through comprehensive assessments of morphological traits, soluble sugar profiles, and activities of key sucrose-metabolizing enzymes (neutral invertase [NI], acid invertase [AI], sucrose synthase [SS] in synthesis and cleavage directions, and sucrose phosphate synthase [SPS]) . Results: One-way ANOVA revealed significant genotypic variation in all measured traits, with sugar accumulation peaking in central fruit sectors and correlating strongly with enzyme activities. Notably, high SS-cleavage activity in 'Jindu No.1' and 'Bai Yulong' facilitated hexose buildup, while elevated SS-synthesis in 'Bicolor Fruit' diverted carbons away from sugars. Principal component analysis (PCA) integrated these traits, ranking quality as 'Bai Yulong' > 'Jindu No.1' > 'White Crystal' > 'Bicolor Fruit' and defining a "high-sugar" metabolic mode characterized by dominant SS cleavage. Discussion: These findings reveal physiological mechanisms driving quality differences and provide actionable biomarkers for molecular breeding of sweeter pitaya varieties, advancing sustainable industry development.