Preferential flow refers to the rapid transport of water and solute through some small portion of the soil volume which is receiving input over its entire inlet boundary. It is a general phenomena but not exception. Preferential flow is confined to many factors, such as macropore in soil, structure, texture, water content, initial water content, application rate of water and solute as well as application method of solute etc.. There are two mechanisms causing preferential flow one is heterogeneity-driven, another is wetting front instabilities-driven. At present, the most reliable methods observing preferential flow are soil coring, soil column effluent experiment and dye tracers. Although it is very difficult to simulate preferential flow, many models were still suggested. The focus of preferential flow research should be put on doing a number of field experiment, so as to obtain enough data to describe preferential flow, developing new observation techniques to monitor preferential flow and suggesting new models to simulate preferential flow. Furthermore, the environmental problems associated with soil and ground water contamination could be solved.