自1909年穆迪将债券评级引入评级体系以来，评级制度在以美国为代表的主要西方国家得到了发展和完善。到目前为止，评级公司的评级业务已经包括信用债券、抵押债券、中期票据、可转换债券、财产担保债券、保险单、有担保的投资合同、优先股以及所有类型的短期债务和银行存款债 Since Moody ’s bond rating was introduced into the rating system in 1909, the rating system has been developed and improved in major Western countries represented by the United States. So far, rating companies have included credit bonds, mortgage bonds, medium-term notes, convertible bonds, property-backed bonds, insurance policies, guaranteed investment contracts, preference shares and all types of short-term debt and bank deposit