CMO is a multi-level transfer securities, which comprehensively embodies the characteristics of installment securities and installment securities. The core technology of bond structure is to create short-term, medium-term and long-term securities according to the future income of supporting assets, so as to reduce the systemic risks faced by investors. A typical CMO generally includes several "normal grade" bonds and one "residual grade" bond, of which the last grade of "normal grade" bonds is also called "Z grade" bonds. "Ordinary" bonds Except for "Z" bonds, the bonds of all grades pay interest at the same time after issuance, but the principal is paid in turn according to the grades. However, the "Z-class" bonds do not pay interest, and the interest is compounded. Only after the previous "fixed-term" bonds are paid off, the "Z-class" bonds begin to repay the principal and interest; Therefore, "Z-class" bonds, also known as interest-bearing bonds, are essentially bonds with a suspension period of principal and interest. After all the "regular grade" bonds are repaid, all the income from the remaining supporting assets will be paid to the "residual grade" bondholders. The characteristic of mortgage-backed bonds is to reorganize the cash flow of the basic loan portfolio by using the term stratification technology and create securities with different term grades. Investors' risks and potential returns increase with the extension of securities term. The typical form of CMO generally includes four kinds of bonds: A, B, C and Z bonds. The cash flow of the loan portfolio is first used to pay the principal of the A-class bonds. When it is fully paid, it will pay the principal of Class B bonds, and then pay the principal of Class C bonds in the same way. A, B and C bonds shall pay interest according to coupon rate from the date of issuance. After the payment of the principal and interest of the three types of bonds in the current period is completed, the remaining cash flow generated by the asset pool can be used to pay the principal and interest of the Z-type bonds. Z bond is a bond with accrued interest accumulation. After the principal and interest of the securities at all levels in front of it are paid off, it begins to enjoy interest and principal income, and the unpaid current interest is accumulated and added to its principal balance. The function of Z-bond is to accelerate the payment of the principal of the former N-bond due to the delayed payment of the interest of Z-bond. Mortgage bonds and secured bonds mortgage bonds refer to the bond issuer's part of the bond issuer's property as collateral through appropriate legal procedures when issuing bonds, and once the bond issuer has difficulties in paying debts, it sells this part of the property to pay off debts. Specifically, mortgage bonds can be divided into general mortgage bonds and physical mortgage bonds. In order to ensure the security of bondholders when the market value of mortgaged assets falls, the value of assets used as collateral or guarantee is usually greater than the total value of bond issuance. When the issuer fails to fulfill its promise to pay interest, the custodian of the mortgaged assets has the right to sell the collateral and repay the net income to the mortgage bondholders. If the net income is not enough to repay the debt, the holder of the mortgage bond will become an ordinary creditor, and the claim for repayment of the unpaid part is equal to that of the credit bond. Guaranteed bonds refer to bonds issued by means of mortgage, pledge and guarantee. Among them, mortgage bonds refer to bonds issued with real estate as collateral, pledge bonds refer to bonds issued with its securities as collateral, and guarantee bonds refer to bonds whose principal and interest are guaranteed by a third party.