The objective of this paper is to study preferential flow and transport rule of nitrate-N in Bai soil profile with the soil coloration analysis and nitrate tracing.The results were as follows: the macropore distribution and preferential flow ways could be analyzed by coloration.The larger colored area indicated higher macropore content in every soil layer.In Bai soil profile,the macropore contents of surface layer were the highest.The macropore contents below the third and the fifth soil layers were low.In farmland,preferential flow was the main ways of nitrate-N transport.The preferential flow could affect to about 78 cm in soil profile.The groundwater was affected obviously by preferential flow and nitrate-N content in groundwater was multiplied more than 10 times in this experiment.