How can we install OS as Windows for 300 clients in a same time?

we can install with the help of windows server WDS

SCCM is also for deployment and many other things. I have pushed the OS for more that 300 machines and it worked perfectly. You have a "new computer" scenario, correct? You need to import machines data into SCCM first, prepare image, create a Task Sequence, make a collection and schedule a deployment. And test it first :)

My friends i meant that how may we install windows OS for the first time on clients in the same time?

SCCM is for upgrading 

you can use sccm in the network 

We can do it with System Center Configuration Manager

my friend if you mean by network, yes that's true