Agricultural non point source pollution is arising more and more attentions as one of the major causes leading to deterioration of water quality. Agricultural non point source pollution assessment is the basis of field management and water pollution control

which is significant when carrying out best management practices to farm ecosystems. An approach for assessing spatial distribution of agricultural non point source pollution in farm ecosystems

taking P as an example

is introduced. An index system is suggested and a sensibility index is introduced to identify the critical source areas in the agriculture regions. The approach needs to be modified based on different conditions to which it is applied.