During the pluin rain period of June-July in 2003,the pH values and concentrations of N,P elements of samples of rainfall,throughfall and runoff in north Taihu Lake were measured.The results showed that the averge pH value of throughfall was 1.2 pH.unit higher than that of rainfall.The effciency of neutralization acidic matter was 82%-97%,The order of abilities of neantral-izatain for acidic rain of different canopy were as following:broadleaf > mix of broadleaf and conifer > conifer.At the same time,the ratios of TN,TP of waters from arbor, lawn, village and small lown to those of rainfall were also calculated.Variations of iron concentrations of rainfall through arbor layer were an active response to acid depostion,i.e.decreasing the degree of acid rain.