A modified PUFF equation of state is proposed with considenation of both non-linear volume change and anisotropic strength of material under compression and dilation.Taking 2-D impact of orthotropic material and thermal shock wave under X-ray radiation as examples,a finite element program is developed.The mean stresses obtained by traditional and modified PUFF equation of state are compared.They are obviously different at low compression and tension states.With increase of stress,they tends to be consistent gradually.