The multiple generations of fast-growing plantation forests have led to decrease in the water holding capacity of the forest land. Soil macropores replenish groundwater in the form of preferential flow and are an important factor in the quantitative study of soil water movement. A water breakthrough experiment was conducted on the soil taking successive planted 1-4 generations of Eucalyptus plantations as the research object, and the water breakthrough curve was drawn. The number of macropores, radius and saturated hydraulic conductivity were calculated with the combination of Poiseulle equation. The characteristics of soil macropore and the effect on the saturated hydraulic conductivity were investigated. The results show the following:(1) the effluent rate of Eucalyptus plantation soils in general showed a uniform increase and then stabilized. The steady effluent rate showed I > II > III > IV and decreasing with the increase of soil depth. (2) The macropore radius ranged from 0.3 to 1.5 mm, mainly concentrated in 0.4-0.6 mm, which significantly decreased with the deepening of the soil layer (p<0.05). The macropore amount ranged from 3.56×10⁴ to 4.81×10⁵/m². With the increase of successive planting generations, the macropore pore size range became smaller and the amount of macropores in the same pore size range decreased. This was the result of the combined effect of soil physical and chemical properties. Soil bulk density ranged from 1.15 to 1.45 g/cm³ and presented a highly significant negative correlation with macropore characteristics. Saturated water content and total porosity were all significantly and positively correlated with macropore characteristics. The organic matter content ranged from 5.43 to 32.33 g/kg and showed a highly significant positive correlation with the macropore characteristics. (3) The saturated hydraulic conductivity of soil in Eucalyptus plantations ranged from 0.41 to 4.50 mm/min, which decreased with increasing successive planting generations. This showed significant correlation with the basic characteristics of macropore. The total amount and mean volume of macropores showed a significantly positive correlation with the saturated hydraulic conductivity of the soil. The fitting equation was y=ax+b, (R² > 0.66), accounting for 66% and 79% of the variability in the saturated hydraulic conductivity, respectively. As a conclusion, with the increase of successive planting generations of Eucalyptus plantations, the pore size of soil macropores decreased, the amount of macropores of the same radius decreased, and the saturation hydraulic conductivity decreased. The infiltration and water conductivity of the soil under the Eucalyptus plantations are weakened, which is prone to soil erosion.