Abstract: This paper studied the relations between the quality of credit assets and the quality of mortgages in the bank credit management. It stated that it was possible to analyze the quality of credit assets through analyzing the quality of mortgages. This paper initiated a new method to study the credit risk and constructed a new index using this method: Mortgage-amending default ratio of assets. This index was testified that it could describe the credit risk effectively through the case study. The paper conclude that this index should be adopted