Hi Mithun,
You can use the method listed in the http://support.smartbear.com/viewarticle/26966/ article to add the script file from another project to your current project. This will allow you to call script routines.
I think another approach will be interesting for you as well. TestComplete provides functions to build your own script extension. You can use this extension as a storage for scripts. The only thing you need to do is to add the script extension to TestComplete's list of extensions. After that, you can call routines declared in this extension from other TestComplete projects. Refer to the http://support.smartbear.com/viewarticle/28456/ article for details.