I'm building an LFS and with a 1.5 GB space and mount it on /lfs directory and building the glibc-2.2.5 in chapter six promt me that the space was full, what I did to solve this problem was to create a new patition, this time I make 4 GB and I still mount it on /lfs directory.
My problem was when I cd into the /lfs directory the contents of /lfs was gone and when I unmount the new partition the contents of /lfs was back.
As what I've learned in linux is that you could resize the directory by mounting a new partition to that directory.
Please help me.

This is not an LFS specific problem, but one around the whole mounting prinicple. As it stands (and I don't think it's likely to change), when you mount a filesystem on a directory, you can only see what is on that filesystem. If you look at it logically, you can see why it makes sense (hint: mounting CD/floppy/NFS/samba onto same directory... not wanting to see lots of files that are irrelevant).

My advice would be:

Mount the new partition somewhere else, and copy all your stuff over, if you wish, then unmount both and remount your new partition in /lfs.

Alternatively, you could copy only a specific part of your current LFS structure (such as /lfs/usr) over to the 4Gb partition, then mount them both: the original LFS partition on /mnt/lfs and the new one on /lfs/usr.

Just some thoughts.