Do i always need to start the new site in django by "django-admin"
Sure. You can definitely copy (or clone with mercurial, git, you name it) your project and make necessary changes and you are done.
Django-admin is just a nice utility to make your django development easier, but it doesn't setup or do anything ultra-special on your project location.
When i need to start new django i use   django-admin startproject  site1 and it then create skeltion files.
Then use syncdb
i want to know if just copy the files from previous site e,g site1 and then rename it to different folder and make necessary chnages in settings and URL and then use syncdb . Will my site work or
I have to use startproject always and it does some database inserting other than making skelton files