Abstract: With a certain nitrate input at the land surface, different nitrate levels in the unsaturated zone can act as a direct proxy of an aquifer vulnerable to nitrate. Improved understanding of different nitrate distribution characteristics in the unsaturated zone and its formation mechanism is important to evaluate nitrate vulnerable of an aquifer and protect groundwater from nitrate pollution. This paper collects data of nitrate content of the only two existing unsaturated profiles in North China, summarizes the differences in nitrate distribution in the profiles, points out that infiltrate rate and denitrification potential are two keys to the differences. Furthermore, future developments in the unsaturated zone, which is quantification of denitrifcaiton potential using isotope techniques are proposed.