In this study, same amount of potassium (240 kg·hm^-2) was applied as basal dressing (treatment 1) and as 1/2 basal dressing + 1/2 topdressing at day 75 after planting (treatment 2), aimed to investigate the effects of potassium fertilization period on the photosynthetic characteristics of edible sweetpotato and the starch accumulation in storage root. As compared with treatment 1, treatment 2 improved the leaf photosynthetic rate and sucrosephosphate synthase activity and the storage root’s adenosine diphosphate glucose pyrophosphortlase  activity, enhanced the starch accumulation rate in storage root (with an average increment of 6.7%), and increased the root tuber yield significantly by 8.2%. Both of the potassium fertilization treatments improved the synthesis of sucrose in leaf and the transformation from sucrose to starch in storage root, as compared with no potassium fertilization.