The water quality in rainfall,throughfall,stemflow and litterthrough in the Pinus sylvestris var.mongolica at Eastern mountainous region in Heilongjiang province has been studied.The indicator include pH,Do,TURB,COND,ORP,K,Na,Ca,Mg,Cu,Zn,Mn and Fe.The results show that the chemical properties of rainfall has been changed after it passing through forest canopy.The pH is lower than those of rainfall.After through litter,the acidification of water is better.The results suggest that the litter of Pinus sylvestris var.mongolica has better buffering ability of water acidification.The change of COND is similar in the throughfall,stemflow and litterthrough.And the average of COND in the stemflow and litterthrough is higher than that in the rainfall and throughfall every month.The average of ORP in the litterthrough is lower than that in the rainfall and stemflow.So the litter of Pinus sylvestris var.mongolica is better to reduse the ORP.And the Pinus sylvestris var.mongolica is better to increase the content of Fe and Mn in the water.