Have you watched breakdawn of twilight? why bella's eye turn into red finally?

Because the Cullens have yellow eyes cause they feed with animal blood. Normal vampires which feed with human blood have red eyes like the Volturi. At least that's what I got from observing the movies.

i didn't watch it yet. i still have works to do.. so busy.. and if i cant really watch it,i probably buy a disc on that,and i surely save a bucks in buying a copy of breaking dawn than watching it in cinemas.. dont want to miss it

she's still full of her own human blood. hence having red eyes.

That's because of two reasons. One: because golden/amber eyes only happens to those who drink animal blood instead of human blood. And second: because she is a newborn vampire. Even if she drinks animal blood, she will still have this eye color. This will change in a few years when she matures (from being a newborn vampire).

The vampires' eyes are only gold if they've been drinking animal blood. Since Bella is a newborn, she hasn't had animal blood yet. The only blood she's really had was when she was pregnant and now she just woke up as a vampire and is probably hungry and that's why her eyes are red.

I haven't seen the movie yet but I plan to do it soon. I think one of the previous answers about the newborn vampire was correct though.:)