Good day Sivakumar!

> Can i take a single ticket from Beiijing to Hongkong and break the journey in 2 day interval ?

No you can not.

> If it is not possible then can i get soft/hard sleeper berths in one or two days advance after reaching the city to next city.probable dates of journey are 20th to 30th september 09.

It is very hard to say. You know from the end of August to the beginning of September is the returning school period for college students. And train is their main travel method. The train tickets can be very hard to get. You need to be prepared.