Under conditions of shallow water table,water flux pass through the root zone boundary is an unneglected component on calculation of water balance.With simultaneous measurements of soil water potential by a serise of tensiometers and of soil water content by neutron probe meter in soil profile,water flux pass through the boundary of root zone can be calculated by zero flux place method.However,if zero flux plane isn't appeared in the profile,it can be calculated by Darcy's formula with measurements of soil water potential near the boundary and soil water conductivities which are obtained beforehand.In a process of irrigation of wheat field by pumping water from well,zero flux plane was found in nonirrigated wheat field near the boundary of root zone,and its depth was followed by the fluctuation of water table.There fore,there was not only upward flux pass through the boundary during this process but also downward flux which was unfavourable for water supply to root system.