An experiment was conducted to investigate the effect of corn and soybean meal with diffrent particle size on feed quality, energy metabolism and growth performance of broilers at different days of age. 288 broilers at 11-day-old and 192 broilers at 24-day-old were divided into six groups per day. The first three groups were used for corn particle size test, and the last three groups were used for soybean meal test. Each group had 8 replicates, and each replicate had four (24-day-old) or six (11-day-old) per replicate. The experimental diets were divided into corn and soybean meal groups. Corn in the corn group was crushed through 1 mm, 2 mm and 3 mm grinding sieve, and other large feed materials were crushed through 2 mm grinding sieve, which was the same in the soybean meal group. The experiment lasted for six days (three days in pre and three days in post-tial). The results showed as follows: ① the logarithmic geometric mean particle size of corn and soybean meal increased with increasing sieve size; the logarithmic geometric mean particle size of soybean meal was larger than that of corn under the same pulverized sieve. There was a linear relationship between the geometric mean particle size of corn and the screen aperture: y=90x+359.33 (P<0.001, R²=0.983), and there was a linear relationship between the geometric mean particle size of soybean meal and the screen aperture: y=110x+359.00 (P<0.001, R²=0.990); the hardness of pelleted feed was significantly reduced with the increase of particle size (P<0.05). ② Different grinding sizes of corn and soybean meal had no significant effect on energy metabolism of broilers at the metabolizable energy level. ③ From day 11 to 16, the FI under 3 mm grinding sieve in soybean meal group was significantly higher than that under 1 mm grinding sieve (P<0.05), and FCR was the lowest of 3 mm grinding sieve in corn and soybean meal groups. From day 24 to 29, FI, ADG, FCR were not affected by grinding sieve. As a conclusion, the particle size has a significant effect on the feed quality, the effect of particle size on growth performance of broilers from day 11 to 16 was more significant than that of broilers from day 24 to 29. It is recommended that the particle size is 3 mm, and logarithmic geometric mean particle size of corn and soybean meal is 638, 681 μm. [ABSTRACT FROM AUTHOR]