The main credit card number of China Bank is different from the subsidiary card number, but they share a capital account. The supplementary card is not a separate account, but a derivative of the main card. With the funds and credit line of the main card, the overdraft amount is finally returned by the applicant of the main card, which is why the person who uses the supplementary card does not need proof of financial ability.

The premise of the existence of the secondary card is that the primary card exists. The consumption repayment and credit record of the secondary card are in the name of the main cardholder, and the credit limit of the secondary card is also set by the main cardholder, which can be a certain proportion of the total credit limit of the main cardholder (it cannot exceed the total credit limit of the main cardholder).