From assembly.. when I import a toolbox component, edit it and save it as a part ,
it always deal with the new saved part as a surface body
How can I deal with it as a solid body ?
With no part, and no screenshot to work with, I have to assume the edit you are making to the part is what causes it to become a surface body.
Either avoid editing it, or discover why it is now a surface, and repair the "defect". Solids usually turn into surfaces when faces are deleted.