The aim of the present work was to evaluate the distribution and concentrations of sugars and acids in vacuole,cytoplasm,and free space in peach fruits,and assess their contribution to sweetness and sourness.Compartmental analysis method was used to calculate the concentration of sugars and acids in vacuole,cytoplasm and free space,and a survey was performed to evaluate fruit sweetness and sourness of peach fruits at harvest.The results showed that sugars (sucrose,glucose,fructose and sorbitol) and acids (malate,citrate,quinate and shikimate) in vacuole,cytoplasm and free space were 27.3,11.6 and 9.0,and 2.09,0.94 and 0.35 mg·g^-1,respectively,in mature fruits.Sucrose and malate accounting for 80.6% and 77.0% of total sugars and acids,respectively,were principal accumulation form in ripe peach fruits.The tonoplast with lower permeability was the most resistant barrier for sugars and acids to release.Sugar and acid contents in different organelles of the block fruit were 3.0∶1.3∶1.0 and 6.0∶2.7∶1.0,respectively,but for the homogenized fruit,the cells were destroyed,so the contents in different organelles were 1.0∶1.0∶1.0;Sugar and acid ratios in vacuoles,cytoplasm and free space were 13.9∶12.4∶23.1,respectively,and the corresponding results in the homogenized fruit were 14.0∶14.0∶14.0,respectively.Evaluation score of the block fruit (2.99) was significantly higher than that of the homogenized fruit (1.98).The differences of sugar and acid contents and sugar-acid ratio in vacuole,cytoplasm and free space may be responsible for the decrease of fruit sweetness.