This paper analyzes affection and factors of public investor's benefit from the reform of equity separation for example 45 companies. Finally， it is discovered that because of the reform of equity separation， public investor's equity value raise up， but company profit doesn't change. After the reform of equity separation， the change of equity construct and circulation of stock market are the primary factors from influencing existing public investor's benefit， therefore it is proved that paying attention to the change of equity construct and circulation of stock market can protect existing public investor's benefit.