Taking rotary tillage(RT)as control，five treatments of subsoil tillage depth of 30，35，40，50 and 60 cm(ST30，ST35，ST40，ST50，ST60)were set up to study the effects of subsoiling depth on aggregate distribution and stability in irrigated sierozem of Gansu Yellow River irrigation area through a 5-year field experiment.The result showed that the aggregation and stability of large aggregates in 0～40 cm soil layer were significantly increased by subsoiling tillage treatments.Compared with RT，under dry sieving，>0.25 mm aggregate content(R0.25)，mean weight diameter(MWD) and geometric mean diameter(GMD)increased by 6.16%，8.53% and 13.38%，respectively，and the fractal dimension(D) decreased by 3.81% by subsoiling tillage.While under wet sieving，R0.25，MWD and GMD increased by 44.78%，10.08% and 5.81%，respectively，and D value decreased by 0.63% with soiling tillage，compared with RT.The percentage of aggregate destruction(PAD)and unstable aggregate index(ELT)of subsoiling tillage treatments were reduced by 5.77% and 5.88% compared with RT，respectively.R0.25，MWD and GMD increased with the increase of subsoiling depth，and the order of the value was ST60>ST50>ST40>ST35>ST30>RT.The aggregate content of different sizes also had the same trend，while PAD，ELT and D showed the opposite order.All the results indicated that subsoiling could significantly improve the content and stability of soil aggregates.The deeper the subsoiling depth is，the better the improvement effect of soil structure will be.In consideration of subsoiling benefit and mechanical power configuration，the subsoiling depth was recommended to be at least 35 cm.