The papers are based on the investment behavior perspective. The private placement companies in 2007 are as the research object. Relationship between ownership structure and investment diversification are comparative analysis of private placement and non private placement from 2008 to 2012. The study finds that there is no significant relationship between company ownership structure of non private placement and diversification of investment. Compared with the private placement companies, separation of ownership of private placement and diversified investment levels negatively correlates. Degree of separation of ownership on private placement with diversified investment is “U” shaped relationship. The institutional investors holding of private placement are positively related to the level of diversified investment. The equity balance degree of private placement and investment diversification is negatively correlated. The findings are not only beneficial to improve the ownership structure of listed companies and improve the company’s competitiveness, but also help to conduct regulatory authorities to strengthen supervision on major shareholders to provide some reference value.