The yield and quality of sweetpotato root tubers can be significantly improved by applying paclobutrazol (PBZ), and sucrose-degrading enzymes play important roles in the development of storage roots of sweetpotato. However, the physiological and biochemical mechanisms underlying PBZ-regulated storage root development is still unclear, and especially it remains to be investigated whether sucrose metabolism is involved in the PBZ-regulated development of storage roots. In this paper, sweetpotato cultivar Kokei 14 was used, a predominant cultivar planting in Hainan. After applying PBZ treatment in the early stage of cultivation (20-30 d after planting, dap), the following phenotypic parameters were investigated at 120 dap including the fresh weight of storage root per plant, fresh weight per storage root and storage root number per plant. To elucidate the physiological and biochemical mechanisms relevant to sucrose metabolism underlying PBZ-regulated storage root development, the following physiological and molecular parameters were also examined in storage roots at different development stages (30, 60, 90 and 120 dap) including the content of starch and soluble sugars (glucose, fructose and sucrose), the activities of sucrose-degrading enzymes and expression levels of the gene families. PBZ increased the yield of sweetpotato by increasing the fresh weight per storage root, but without affecting storage root number per plant. PBZ increased the content of soluble sugar and starch in storage root. However, the effect of PBZ on the yield and quality of storage roots only occurred in the early stage (30-60 d after planting) after treatment, and in the late stage (90-120 d), PBZ treatment had no significant effect on yield and quality. PBZ treatment significantly increased the activities of sucrose synthase (Sus), cell wall invertase (CWIN) and cytoplasmic invertase (CIN). However, PBZ had no significant effects on vacuolar invertase (VIN). As compared to CWIN and CIN, Sus activity was induced by PBZ treatment much earlier and more dramatic. Sus activity was significantly induced at 30 dap, whereas the activity of CWIN and CIN were significantly induced at late stage i.e. 60 dap. In other periods (especially 90-120 d), PBZ treatment had no significant effect on the activities of Sus, CWIN and CIN. The determination of the expression level of Sus, CWIN and CIN genes showed that IbSus2, IbSus5-7 and IbSus9 highly expressed in storage tuber were all significantly induced by PBZ at 30 dap. IbCIN3, IbCIN7 and IbCIN8 expressed in storage roots, and IbCWIN2 and IbCWIN4 expressed in storage roots were significantly induced by PBZ at 60 dap. However, in other periods (especially 90-120 d), PBZ treatment had no significant effect on the expression level of the relevant genes. It is speculated that the increase of Sus expression and activity under PBZ treatment is earlier and more dramatic, which can promote the rapid and biosynthesis and accumulation of starch and the rapid expansion of storage roots, while the subsequent increase of CWIN and CIN expression and activity can increase the content of soluble sugar in root tubers thus improving the quality of storage roots, and can also provide energy supply for starch biosynthesis and storage root expansion. The specific members of Sus, CWIN and CIN genes induced by PBZ had also been identified. Notably, the effects of PBZ on the yield and quality of storage roots, and activities and gene expression levels of sucros-degarding enzymes in storage roots mainly occurred in the short period after PBZ treatment. With the extension of time, the effects of PBZ on the above indicators gradually disappeared. Therefore, in order to improve the yield of sweetpotato in production, it is necessary to conduct PBZ treatment throughout the entire growth period of sweetpotato. The above results can provide a theoretical basis for achieving high-quality and high-yield sweetpotato production by variety breeding or cultivation measures.