Fractionation of a soil sample for soil aggregates of different size grades (>2, 2～0.25, 0.25～0.053 and < 0.053 mm) was carried out using the wet screening method for the study on effects of application of corn stalks on quantity and structural characteristics of humic acid in aggregates of the soil incubated indoors at a constant temperature of 25℃. Results show that after the application and incubation, aggregates of size fractions 2～0. 0.25 mm and >2 mm turned out to be dominant in the soil accounting for 51.41% and 34.12%, respectively, on average. Their total carbon content ranged in 10.15～25.74 g kg^-1, and their absolute HA content in 4.06～5.79 g kg^-1, obviously higher than what was in the control, and the differences got bigger and bigger with the application rate of corn stalks; However, the C/H and high/medium temperature exotherm ratios were lower in all the treatments than in the control, and negatively related to application rate of corn stalk, which suggests that higher corn stalk application rate makes HA molecules less condensed and simpler in structure.