Abstract　 　　
　Galaxies are categorized into two main populations, red quiescent galaxies and blue star-forming galaxies. One of the key questions is which physical mechanisms are responsible for quenching star formation activities in blue galaxies and the resulting transformation? In this talk, I present research on the properties of “green valley” galaxies in the COSMOS field and to constrain mechanisms that lead to star formation quenching. In the end, I will show our new progress about two-dimensional optical spectroscopy of nearby galaxies with MMT and the NAOC2.16m telescope, and discuss how does this project provides constraints on galaxy formation scenarios.