Heavy ion collision is a powerful tool to study the fundamental
structures of the QCD phase diagram. Experiments at first ten years at
Relativistic Heavy Ion Collider (RHIC) is to mainly study the
properties of the Quark Gluon Plasma (QGP) at top energy
($sqrt{s_{NN}}$ = 200 GeV), where the baryon chemical potential is
small. The first phase of Beam Energy Scan (BES) program successfully
carried out at RHIC in year 2010 and 2011. The main goals of the BES
program at STAR experiment are to search for the phase boundary from
the parton to hadron degrees of freedom, and to search for the
critical end point. Experimentally, it is possible to access finite
baryon chemical potential in the QCD phase diagram by varying the
colliding beam energies in heavy ion collisions.

In this talk, I will show the recent results from the BES program at
STAR. I will review several key signatures of the QGP at top RHIC
energy, then discuss what we observed during the first phase of the
BES program at RHIC.