There may be the following situations when a China Merchants Bank credit card is deducted 198 yuan per month:

1. Repayment: If you use a China Merchants Bank credit card for consumption, the monthly bill The amount you need to repay will be listed. If you do not repay the full amount before the repayment date, the bank will automatically debit your bank account. If you are deducted 198 yuan per month, it may be because your bill balance is approximately 198 yuan per month.

2. Annual fee: Credit cards usually charge an annual fee, which is to maintain the credit card services and additional benefits. If your China Merchants Bank credit card is charged 198 yuan every month, it may be because your credit card has been charged an annual fee.

3. Installment payment: Some credit cards will provide installment payment service, and you can pay larger amounts of consumption in installments. If you choose to pay in installments, the corresponding amount will be deducted each month according to the installment plan.

In order to answer your question accurately, it is recommended that you check your credit card bill details, or contact China Merchants Bank customer service for an accurate answer.