The optimum reducing sugar determination conditions of 3,5-dinitrosalicylic acid colorimetry(DNS colorimetry) were investigated using the Response Surface Method(RSM).The reducing sugar content in apple was obtained under the optimum extraction conditions.Based on the results of the single factor experiments，an optimization procedure was carried out in order to investigate the effects of key parameters on reducing sugar determination.Optimization was conducted using a Central Composite Design(CCD) with three key factors of DNS amount，reaction temperature and coloration time.The quadratic term model of the determination conditions was established and the reliability was checked.The results of regression analysis presented a non-significant lack of fit(P=0.133 7) and a high coefficient of determination value(R2) of 0.957 4 for the response surface model,which showed a satisfactory agreement of the polynomial regression equation with experimental data.The influence of three factors followed the sequence as：DNS amount > reaction temperature > coloration time.The optimum determination conditions of reducing sugar using DNS colorimetry were DNS amount：4.0 mL，coloration time：5.0 min，reaction temperature：87.0 ℃.The actual concentration of reducing sugar was obtained to be 94.66 mg/L,which was consistent with the theory predicts under the optimal conditions.According to the optimum determination conditions，the precision，repeatability and accuracy of the method were verified using apple，peach，grape，hami melon，navel orange and pineapple as representative fruits.The standard deviations，relative standard deviations and recoveries of the reducing sugar contents in the 6 fruit species were in the range of 0.1%–0.5%，2.0%–4.8%，90.6%–104.2%，respectively.The study provided a reliable method for accurate，efficient and cost-effective detection of reducing sugar contents in fruits.