I think it is grammatical with one exception: you should include an “it” before “was the poorest so that you have a subject (the pronoun “it”, which refers back to “the import and export performance”) to go with the verb “was”.

Thank you.

It is in passive voice, it's better to get right to the point. I suggest: In 1996, the import and export performance was outstanding, while the performance in 1998 was the poorest. Jennifer has it right, but there are many ways to write a sentence like this.

No. My suggestion is: It is evident that the import and export performance in 1996 was outstanding and that in 1998, it was the poorest.