Please let me know about the open source block diagram making software in which i can show up the functionality of my system.let me know ASAP.

 

Hello,

Have a look a DIA:
https://en.wikipedia.org/wiki/Dia_(software)
Here is the homepage of the software:
http://dia-installer.de/index.html.en

Bertus

 

Gliffy is an online Visio alternative. I've used it to make block diagrams.