In this paper, effects of freeze-thawing and dry-wetting processes on the formation of soil macropores and preferential flow under simulative conditions in laboratry, and preferential migration of linear alkylbenzene sulfonate (LAS) in soils growing rice and soybean in field lysimeter were studied. Results showed that both freeze-thawing and dry-wetting processes could cause macropores and preferential flow in soils and that the former was stronger than the latter.The duration of preferential penetration of LAS through 1.5m soil monolith was 23 days for both soils growing rice and soybean. However, their leachate volumes of preferential penetration were much different, i. e., 69 mm for soil growing rice and only 9 mm for soil growing soybean. Preferential migration process was not governed by soil adsorption/desorption processes. The leachate volumes in equilibium governed by adsorption/desorption processes in soil were very similar for rice (185mm) and soybean (178mm).The duration of preferential penetration of LAS was 21 and 35 days ahead of equilibium penetration for soils growing rice and soybean, respectively. The peak concentrations of preferential penetration of LAS amounted to 20%-30% of peak concentration of equilibrium penetration in soil growing soybean. This ratio was as high as 30%-86% in soil growing rice. This phenomenon of preferential migration could not be obsearved in repacked soil monolith without macropores.