正是在1998年春天他来到了上海。（强调句）翻译成英文

It was in the spring of 1998 that he came to Shanghai.
It + be + ... + that ...句型中的be的时态要与所强调的句子的时态保持一致。这个句子中的时态根据in the spring of 1998来判断，强调句型中的be应该用 was.

强调句句型其中之一是:It is(was)+ 强调部分+ that + 其它部分
这句话就可以用此句型：
It is in the spring of 1998 that he came to Shanghai.

It was in the spring of 1998 that he came to Shanghai.
it is ... that ...这是强调句

楼上两句时态前后矛盾

It's spring of 1998 when he came to Shanghai

It is in the spring of 1998 that he get to Shanghai.

It's exactly that he came to Shanghai in the spring of 1998.