@qiyunfeng, TurboTax Online activation code can be activates/associated to your online account only once. If you already activate the product, you cannot do it a 2nd time or in another account. All returns needs to be done in this account. At the top of your Welcome page, when you sign in, you'll see your return's counter with what is available for your code (ex: 8 returns available on 8).
As long as you stay in the same TurboTax Online edition (example: Deluxe), you won't have to pay at the end. The software will ask you if you want to apply the return to your code. If it's asking to pay even if you activate your code, it should be because you had to upgrade in a higher edition or you add other products, like Assist & Review.
Thank you for choosing TurboTax.
