Abstract: Warm dense matter exists throughout the universe,such as in the evolving surface layers of stars or in the inner cores of giant planets, and this state of matter influences our daily life deeply (as in the production and propagation of our Sun's light).This extreme state of matter cannot be explained by traditional condensed matter physics or plasma physics, since it lies between the classical and quantum states.Recently,with the fast development of high power lasers,it has become possible to conduct experiments and test theories of the warm dense state.The existing theory developed for the corona plasma does not work well in this regime,but X-ray Thomson scattering has recently been successfully used in its diagnostics.A new theory is also required to analyze the experimental data.