when i buy an application from apple store.they always charge me 1.98E plus price of application.Please resolve my this issue.Thanks.

Do you add or change the credit card details on your account each time you purchase something ? If you do then you will receive a temporary store holding charge to check that the card details are valid and that the card is active - the charge should disappear from your card within a few days (though it might take a day or two longer due to the weekend)

Store holding charge : http://support.apple.com/kb/HT3702