Your using a solid filled box in the simulation? Or are they empty boxes. A zero thickness box would give you bad results.
If you just want to hide a face that its not used use 'delete face'
I'm not sure i quite understand your situation.
Why do you want to hide the face after you've meshed?
In fact, I am stimulating a ship enclosed structure, just like a box with many internal ribs.
The components are all Surface so can create mesh easily than a Solid body.
After finishing the mesh, I have to flip shell element.
So I would like to hide the external mesh face and see the internal mesh detail.
The mesh face can be hidden if I create a structure model in part file.
However once I insert those structures and mate together in Assembly, I cannot hide the selected mesh face.
I don't know what's wrong is it.
I don't think I understand what you are doing, but if you are mating several of these boxes together and then hide one of the mating faces, the other mating face would still be visible, blocking visibility to the inside of the box. I doubt this is what you are talking about, but it might be something that simple.