Taking the data of A share listed companies from 2010 to 2013 as a sample, this paper makes an empirical test on the effect of investor’s entry on the relationship between managerial power and non-efficient investment. The empirical results prove that managerial power and non-efficient investment show a stronger positive correlation, but the positive correlation decreases, to some extent, with the joining of institutional investors. The further study distinguishing the different institutional investors finds that the pressure-resistant institutional investors can weaken the positive correlation of managerial power and non-efficient investment, but the pressure-sensitive institutional investors do not play such a role.