According to the general principle of molecular dynamicstheory and the Lennard-Jones Devonshire(LJD) liquid theory, H.S.Tsien givenan fundamental equation of state for gases at high temperatures andpressures. Tsien's EOS has physical foundation, high accuracy eqlicit temperature, and simple form. In this paper, we tested the applicability of LJD liquid theory inhigh-temperature and high-pressure gases by constant volume-temperaturemolecular dynamics, and obtained exact MD calculations for high temperatureand pressure gases EOS. Based on the MD exact numerical solution. TheAAD between theaso data and the improved Tsien's Eos cesults is less than 10%.in high density vesign.