hugou,
The break dependency option in the reference viewer is only available if the dependency is no longer needed, so it wouldn't work for what you're doing.
Normally your best option it to go through your part and redefine your references to reference a coordinate system or independent feature. With a copy of a face this option will not work. You would have had more options if you copied whatever features defined the face initially (copy the boundary blend for instance, rather than copying the geometry of the resulting surface).
Is the face you are trying to copy from an imported feature that isn’t in Pro/E format? You could try importing the geometry that you are trying to copy into your working model, then use the import data doctor (IDD) to remove all of the surfaces except for the one you are trying to copy. This would give you the same effect as importing a model then copying a surface and then deleting the original.
-Funi