英汉词典

Do is used as an auxiliary with the simple present tense. Did is used as an auxiliary with the simple past tense. In spoken English, negative forms of do are often shortened, for example do not is shortened to don't and did not is shortened to didn't.
do 是用于一般现在时的助动词，did 则是用于一般过去时的助动词。口语中，do 的否定式通常用缩合形式。例如，do not 略作 don't，did not 略作 didn't。