The formation and evolution of galaxies is one of the key questions in today’s galaxy physics. We have investigated two important phases in galaxies evolution scenario: the stage of luminous infrared galaxies (LIRGs) and the transition phase from IR-QSOs to classical optical QSOs. In order to investigate the transition phase from IR-QSOs to classical optical QSOs, we selected the type I QSOs with obvious host component and investigating the properties of their host galaxies. With the help of the stellar population synthesis code STARLIGHT, we determine the luminosity fraction of AGN, stellar population ages and star-formation history (SFH) of host galaxies. We find out that there is a correlation between the star formation history and AGN property, which is consistent with a co-evolution scheme for black holes and host galaxies.
