The main card and supplementary card of a credit card are generally used between a family. Credit card holders are generally parents, and supplementary cards are generally applied by parents for their children, but the children must be 14 years old. The main card and the auxiliary card must have the same card type, and the credit limits of the two credit cards are shared. After spending with the secondary card, it will not be charged separately, but will be included in the main card. In addition, the secondary card can also enjoy the same preferential annual fee policy as the main card.