I want to install some packages without internet connection.
Please suggest the ways to copy already installed packages on "System1" to "System2" (System2 without internet connection).
Copying files
Take a look at /var/cache/apt/archives
. You could copy them to System2 using a USB disk or via ssh (if it has local network access).
This might not work if your don't repeat this each time you update System1, because you might miss dependencies which were installed in the meantime. So: Not recommended.
Local network mirror
Also, you could setup a local network apt mirror, which is possibly the best solution.
Create a CD or USB-Disk
For this, try APTonCD, reprepro or AptMedium. All do more or less the same - choose your flavour.