Abstract: Abstract: The importance of macropore flow as a preferential flow mechanism for infiltrating water and transport of solutes has been generally recognized during a couple of decades. Macropore flow plays significant roles in the structured soil, such as leading to more infiltration and thus reducing overland flow and rapidly transferring pesticides and other pollutants through the soil macropores into the groundwater. Due to its critical effect on field-scale soil water flow and transport of contaminants in soils, macropore flow is gaining more interest. In this study, soil samples were collected at depths of 0-20 cm and 20-40 cm from sloping cropland of purple soil, which are located at Yanting Agro-ecological Experimental Station of Purple Soil (105?27?E, 31?16?N), hilly central Sichuan, Southwest China. Using Br- tracer and simulated rainfall methods, lab-scaled disturbed and undisturbed soil column experiments were conducted to characterize the preferential transport behavior and evaluate the contribution of preferential flow based on simulations with the CXTFIT model. The breakthrough curves (BTCs) for each soil column were also obtained by analyzing the dynamics of Br- in the outflow. The integrated parameter, PFSP, defined as the ratio of extended quantity of BTCs due to preferential flow to extended quantity of BTCs caused by hydrodynamic dispersion and two-region effect, was calculated based on BTCs and CXTFIT datasets of the undisturbed soil columns. The BTCs of undistributed soil column showed an early breakthrough of Br- and also an upturned tail, indicating the presence of both preferential flow and matrix flow in studied soil. The preferential flow contributed 66.2%-68.5% of water discharge and 62.3%-66.1% of cumulative Br- discharge from undisturbed soil columns collected at the 0-20 cm depth, and at the 20-40 cm depth, their contributions was 0.2%-1.7% and 14.5%-20.5%, respectively. These implied that preferential flow made a much greater contribution to cumulative Br- discharge for the soils at the 0-20 cm depth compared to the soils at the 20-40 cm depth. Transport parameters of Br- were obtained by fitting its BTCs in the soil column with two-region model and CXTFIT software. It was found that the values of pore velocity and hydrodynamic diffusion coefficient for the soil at the depth of 0-20 cm were higher than those at 20-40 cm depth, while the retardation factor, with higher value indicating more preferential flow developed in the soil, showed contrast trend for the 2 depths. This was due to the fact that Br- quickly migrates with preferential flow through soil macropores, which may weaken the retardation effect. As for the dynamic watershed scale factor, the value was higher at the depth of 0-20 cm than that of 20-40 cm, indicating the higher percentage of flowing water in the soil column collected at 0-20 cm depth that has better developed preferential flow. The mass transfer coefficient value of the undisturbed soil column taken at 0-20 cm after plowing activity was the lowest, while the values were close among other soil columns. The PFSP value, which can ascertain the contribution of preferential flow out of other mechanisms, revealed that macropore flow made the biggest contribution to the extended quantity of BTCs, two-region effect made the second and hydrodynamic dispersion made the third, indicating PFSP can be a useful index to quantify the contribution extent of macropore flow.