hi, i have problem with my apple id when i want purchase app even free one, asked me for complete my card informations... but i don't want to use debit card because already i have gift card and charge it in my id... please help

Though you are being asked for card details it doesn't necessarily mean that the card will be charged for the purchase (unless you want to gift content). Have you tried entering your card's details to confirm the account ? You should then be able to remove it.

From http://support.apple.com/kb/HT5582 :

When making purchases, content credits are used first, followed by Gift Certificate, iTunes Card, or Allowance Account credits; your credit card or PayPal account is then charged for any remaining balance

Is it a new account ? If it is then unless a new account is created by following the instructions on this page (the instructions won't work with existing accounts) : http://support.apple.com/kb/HT2534

then you will need to enter card details (debit cards are no longer accepted in all countries) before the account can be used to download any item from the store.