英语没有大门怎么说怎么写

In Engpsh, we would say "There is no main entrance." or "The building has no main entrance." or "The entrance is not designated as the main entrance."

Here are a few ways you could write it:

"There is no main entrance to the building."
"The building does not have a designated main entrance."
"There is no entrance that is marked as the main entrance."