英语反转很大的广告怎么说

If you are referring to a "reverse" ad that is very large, you might say "This is a massive reverse advertisement." Alternatively, you could say "This reverse ad is huge," or "This is a huge reverse advertisement."

It is important to note that the term "reverse ad" may not be widely understood, so it might be helpful to provide more context or explain what you mean by "reverse ad."