This study investigated the effects of four potassium-containing fertilizers (complex fertilizer, potassium nitrate, potassium sulfate, and potassium dihydrogen phosphate) on sugar and organic acid metabolism in grape fruits. The results showed that all four fertilizers increased the activity of sugar and organic acid metabolism-related enzymes at all stages of grape fruit development. During the later stages of fruit development, these fertilizers increased the total soluble solid content and the sugar content of different sugar fractions while decreasing the titratable acid content and organic acid content of different organic acid fractions. Specifically, potassium sulfate and potassium dihydrogen phosphate had the best effects, increasing the total soluble solid content by 3.5 and 3.4 percentage points, respectively, and decreasing the titratable acid content by 0.18 and 0.17 percentage points, respectively, compared to the control. Transcriptome analysis revealed that applying potassium-containing fertilizers enriched genes involved in pathways related to fruit quality, such as carbon metabolism, carbon fixation, glycolysis, gluconeogenesis, and fructose and mannose metabolism. The fertilizers also affected the expression levels of genes regulating sugar metabolism and potassium ion uptake and transport. Overall, potassium-containing fertilizers promote sugar accumulation and reduce acid accumulation in grape fruits, with potassium sulfate and potassium dihydrogen phosphate showing the most significant effects.This study investigated the effects of four potassium-containing fertilizers (complex fertilizer, potassium nitrate, potassium sulfate, and potassium dihydrogen phosphate) on sugar and organic acid metabolism in grape fruits. The results showed that all four fertilizers increased the activity of sugar and organic acid metabolism-related enzymes at all stages of grape fruit development. During the later stages of fruit development, these fertilizers increased the total soluble solid content and the sugar content of different sugar fractions while decreasing the titratable acid content and organic acid content of different organic acid fractions. Specifically, potassium sulfate and potassium dihydrogen phosphate had the best effects, increasing the total soluble solid content by 3.5 and 3.4 percentage points, respectively, and decreasing the titratable acid content by 0.18 and 0.17 percentage points, respectively, compared to the control. Transcriptome analysis revealed that applying potassium-containing fertilizers enriched genes involved in pathways related to fruit quality, such as carbon metabolism, carbon fixation, glycolysis, gluconeogenesis, and fructose and mannose metabolism. The fertilizers also affected the expression levels of genes regulating sugar metabolism and potassium ion uptake and transport. Overall, potassium-containing fertilizers promote sugar accumulation and reduce acid accumulation in grape fruits, with potassium sulfate and potassium dihydrogen phosphate showing the most significant effects.