Abstract:To explore the characteristics of soil structure and organic carbon distribution in aggregates with fallow year, soils (0-20 cm depth) under 1, 2, 3, 5, 10, 15, 20 fallow years and under clean tillage (as control (CK) were sampled from Lüliang mountains in Loess Plateau, aggregates were separated by dry and wet sieve methods respectively, and then mechanical-stable and water-stable aggregates, organic carbon contents in soils and aggregates were determined and compared. The results showed that within 3a fallow, aggregate content changed irregularly, then the content of water-stable macro-aggregates (>0.25 mm aggregate content, R>0.25), MWD and GMD of aggregates gradually increased with the increase of fallow year, and it accounted for 69.6% of the total aggregate of water-stable macro-aggregates in 20a fallow, 55.2 percent points higher than CK. The contents of organic carbon in soil and aggregates decreased first and then increased with the extension of fallow year, soil total organic carbon (TOC) in 20a fallow reached 7.88 g/kg, organic carbon in aggregates increased first and then decreased with the decrease of aggregate size, mainly concentrated in 1-0.25 mm aggregates. Organic carbon in mechanical-stable macro-aggregates accounted for 54.3%-82.2% of soil TOC, which were 25.0-52.9 percent points higher than CK (29.3%), organic carbon in water-stable macro-aggregates accounted for 17.7%-71.8% to soil TOC, and other plots accounted more than CK (21.1%) except 1a and 3a fallow. MWD and R>0.25 of water stable aggregates were extremely significantly correlated with soil TOC (P<0.01), and GMD of water stable aggregates was significantly correlated with soil TOC (P<0.05). R>0.25 of water-stable aggregates was extremely significantly correlated with organic carbon in 2-1, 1-0.25 and <0.25 mm aggregates (P<0.01), and significantly correlated with organic carbon in 5-2 mm aggregates (P<0.05). In conclusion, natural recovery promotes the increase of organic carbon in soil and in water-stable aggregates, thereby improves the stability of aggregates.