  Quantum molecular dynamic simulations are introduced to study the shock
compressed oxygen. The principal Hugoniot points derived from the equation of
state agree well with the available experimental data. With the increase of
pressure, molecular dissociation is observed. Electron spin polarization
determines the electronic structure of the system under low pressure, while it
is suppressed around 30 $\sim$ 50 GPa. Particularly, nonmetal-metal transition
is taken into account, which also occurs at about 30 $\sim$ 50 GPa. In
addition, the optical properties of shock compressed oxygen are also discussed.
