migrate one wordpress single site to one blog of wordpress multisite

Hello,
Please show me how to migrate one wordpress single site to one blog of wordpress multisite .
I've tried to use plugin"WordPress Importer":
- Export from wordpress single site (. xml file)
- After that import it to the blog of wordpress multisite.
But all images is lost ( not show) in the blog of multisite , don't see any images in media area.
Thanks