I need to install ubuntu 0n more than 300 PC. So is there any way to install it simultNIOUSLY.
If you are looking for a managed/centralized/GUIfied way to do this, take a look at MAAS from Canonical:
Especially if you want to tether your deployment plan to security policies, or deploy configurations using Puppet or a similar tool.
Also check out Landscape for post-deployment updating, scripting, and health checking.
Otherwise look to the links provided by @muru and @AzkerM in comments for more traditional PXE.