In order to protect the interests of investors, fund investment must follow the principle of portfolio investment, even a single market fund can not only buy one or two securities. The terms of some funds expressly stipulate that the investment portfolio shall not be less than 20 varieties, and the purchase of each kind of securities has a certain proportion limit. Investment funds make a mickle, so they have the ability to invest in dozens or even hundreds of securities. Because of this, the fund risk is greatly reduced.