Abstract: The moisture negativeinfluence mechanism of main shelterforest tree species on farmland in Xuhuai plain area was studied.The results are as follows:(1)The wheat at the north side of shelterforest belt had a lower output.It is much lower than that on contrast district and also lower than that at the west side of forestbelt.(2)The diurnal change of transpiration intensity of wheat showed that the low intensity in morning and evening and high at noon,keeping up with the diurnal change of the sap flow of poplars.(3)Wheat’s transpiration intensity had a relatively unanimous variation with sites and time in a day.The wheat nearby the shelterforest belt had low transpiration intensity.With the increase of the distance from the shelterforest belt the transpiration intensity went up gradually.At the positions of 0.7 H and 1.0 H(H means the height of the shelterforest belt) the change of transpiration intensity became steady.This accorded with the law of negativeinfluence.