Metals are not expected to exhibit ferroelectricity because the itinerant electrons screen local dipole moments and prevent ferroelectricity.Recently, the first explicit success of ferroelectric metal has been experimentally realized in LiOsO3.LiOsO3 remains metallic behavior while it undergoes a second-order phase transition at Ts=140K similar to insulating LiNbO3.By performing density functional theory we investigate the lattice instability and electronic structures of LiOsO3, the local polar distortion is due to the instability of the Li ion exclusively.