Since your subject line is "mehtab", it's likely that only people with the name of "mehtab" will bother to read it.
You should use a meaningful subject line in your posts.
"mehtab" is not helpful.
"help me" is not helpful.
"Line tracking robot using microcontroller" IS helpful.
This link: http://tinyurl.com/5s49rjl
will help you.
A more specific link: http://tinyurl.com/3upsb88
i dont understand that the tranmitter will reflect thr IR ray and receiver will receive it in any where..
but it just follow the black line???
whta its mean??
No, the transmitter and receiver need to be located pretty close to each other.
Some of the analog designs I've seen use two transmitters and two receivers side by side. If one of the receivers doesn't get as much reflected light, the 'bot steers in that direction.