1. Different functions: the master card is the master card of an account, which can perform all transaction operations, such as deposit and withdrawal, transfer, etc. The secondary card is an accessory card of the main card, which is mainly used to assist the main card in transactions, such as home use or specific consumption places.

2. The credit limit of the main card is usually higher than that of the auxiliary card, and the credit limit can be set independently. The credit limit of the auxiliary card is usually controlled by the main card and cannot exceed the credit limit of the main card.