This study was conducted to establish the method for determining the released amount of reducing sugar of feed ingredients digested with simulated digestion system to mimic the digestion of pigs, which provided a reference for the evaluation of feed nutrient bioavailability. A corn-soybean meal mixture (75% corn+25% soybean meal) was formulated to test the linear relationship between the released amount of reducing sugar and sample volume. Five treatments of sample volume were consisted of 0.2, 0.4, 0.6, 0.8 and 1.0 g. Each treatment contained 4 replicates with 1 digestion tube per replicate. Corn-soybean meal mixture, barley, peanut meal and rice bran were used to test the repeatability of the method. Each sample was determined for 3 batches with 4 replicates in each. There were 19 treatments to test the additivity of the method. Treatments 1 to 7 were corn, barley, sorghum, soybean meal, peanut meal, cottonseed meal and rice bran, respectively. Treatments 8 to 19 were 12 mixed feeds formulated with 2 or more than 2 kinds of feed ingredients at different proportions. Each treatment contained 4 replicates with 1 digestion tube per replicate. The released amount of reducing sugar of each treatment was determined after the feed was digested with simulated digestion system to mimic the digestion of pigs. The results showed as follows:when the sample volume ranged from 0.2 to 0.8 g, a significant linear relationship (R²=0.999 2) was observed between the total released amount of reducing sugar and sample volume, and the relative released amount of reducing sugar ranged from 559.56 to 582.70 mg/g DM with a coefficient of variation (CV) of 1.66%. However, the released amount of reducing sugar of 1.0 g sample was 5.37% lower than the mean of 0.2 to 0.8 g sample. The CV of intra-batch, inter-batch and total for the released amount of reducing sugar were all less than 1.68%, and the inter-batch maximum relative difference among repeated determinations were 0.68%, 1.50%, 1.39% and 0.29% for barley, peanut meal, rice bran and corn-soybean mixture, respectively. The determined values were greater than the calculated values of the released amount of reducing sugar in 12 mixed feeds (P<0.05). However, the linear regression model of calculated values and determined values of the released amount of reducing sugar was consistent to the line of y=x (P=0.480 5 for intercept; P=0.514 1 for slope). It is concluded that a significant linear relationship is found between sample volume and the released amount of reducing sugar when the sample volume ranges from 0.2 to 0.8 g; the repeatability and additivity of the released amount of reducing sugar of feed ingredients determined with simulated digestion method for pigs can meet the basic requirements of quantitative analysis.