1.主系表结构的句子 　　Iamateacher.-----Iamnotateacher. 　　HeisinBeijing.-----HeisnotinBeijing. 　　Weareclassmates.-----Wearenotclassmates. 　　Itwascoldyesterday.-----Itwasnotcoldyesterday. 　　这些句子中都有系词,am,is,are,was,were,只要在系词后面+not,就变成否定句了. 　　2.主谓宾的句子 　　Herunsfast.-----Hedoesn'trunfast.主语是三单人称,do也要用三单形式does 　　Theylearnfromme.------Theydon'tlearnfromme. 　　Wewenttoschoolbybike.-----Wedidn'tgotoschoolbybike.谓语动词是过去式,do也要变过去式did 　　这些句子中都有谓语动词,只要在主语后面+do的适当形式+not就行了. 　　3.句中有助动词或情态动词的 　　Iwillgetupearliertomorrow.-----Iwillnotgetupearliertomorrow. 　　Shecandancewell.-----Shecan'tdancewell. 　　Hehasgoneabroad.------Hehasnotgoneabroad. 　　只需要在助动词或情态动词后面直接+not,就可以变否定句了. 　　OK?希望能帮到你啊!