Based on the banks' credit risks, we have built an adverse selection model to examine banks' policies when issuing subordinated debts. The result shows that banks with lower credit risks are more likely to issue subordinated debts, since after the issuance, the yields of these debts are lower. When depositors observe the lower yields of the subordinated debts, they would presume that these banks have lower credit risks. As a result, banks with lower credit risks can decrease their operational costs by issuing subordinated debts. This model has demonstrated that the market can discipline banks indirectly through the issuance of subordinated debts.