Through the research on the the controlling effects of shelter forest on nonpoint source pollution of agricultural lands in Taihu Lake area,we get some conclusions:The transfer and loss of N and P(main water pollutants) vary with means of rotation,types of crops and the amount of fertilizer.Shelter forest betweens farmlands and ditches can effectively stop and purify such elements as N and P in soil runoffs,thus controlling nonpoint source pollution of agricultural lands.Poplars with the characteristics of quickgrowing and high value are suitable to be planted as shelterforest in Taihu Lake Watershed.Based on the model of shelter forest,the width ratio of farmland to shelter forest is either between 100∶40 and 150∶40 or between 150∶60 and 200∶60. Such a model can not only save more farm land,but also purify water quality and protect ecological environment.