After doing a clip in a layer in ArcMap if I use the Save As to save the map, the size of the new map is bigger than the old one .
Why the size of a map mxd changes?
I've moved your post into the Mapping space. You will get a much better answer here as the GeoNet Help is intended for community help and feedback. You can see more on the community structure, and what topics are under each space from the following documents:
GeoNet Community Structure
ArcGIS Discussion Forums Migration Strategy
Retrieving data ...