一般来说，把英语句子改为否定句，只要加上否定词not就可以了。
英语否定句是表示否定的句子，必须有否定词。有了否定词才算否定句。英语否定句是中国人学习英语的一个重点，也是一个难点。唯有突破这类难点，才能使我们的英语学习有质的飞跃。
句中有be动词(am/is/are/was/were)的，在be动词后加not。如：I can swim.——I can't swim.He is a math teacher. → He is not a math teacher.
句中有情态动词的(can/should/must/would)，在情态动词后面加not;如：There will be a new building next year. → There will not be a new building next year. (will not可以缩写为won’t)
句中没有be动词和情态动词的，在动词前加don’t或doesn’t句中动词为原形的，加don’t .如： I like apples. I don’t like apples.句中动词为三单式的，加doesn’t，并将三单式的动词还原成原形。如：He likes apples. He doesn’t like apples.
肯定句中的some在否定句中应改为any如：There are some students in the classroom. There are not any students in the classroom.
特殊形式的否定句
肯定句含有every-的合成词时，变否定句时改为no-。如：Everything is ready.→Nothing is ready.
肯定句中含有always， usually和ever时，变否定句时改为never。如：He is always late for school.→He is never late for school.
肯定句含有many，much时，变否定句时分别改为few，little。如：Many students know him.→Few students know him.
肯定句中含有still时，变否定句时应改为no longer。如：Tom is still in bed.→Tom is no longer in bed.
肯定句含有both， both...and，all时，变否定句时应改为never，neither...nor，none。如：Both of us are students.→Neither of us is a student.
肯定句含有nearly， almost时，变否定句时应改为 hardly。如：Lily nearly knows him .→Lily hardly knows him .
肯定句含有“形容词+ enough”时，变为否定句时应改为“too +形容词的反义词”。如：He is short enough to reachit.He is too tall to reach it.
