The sound velocity of the materials at sufficiently high pressure is an important quantity reflecting material qualities under extreme conditions. In this paper, from the shock adiabatics and the Gruneisen equation of state, an isentropic, which corresponds to shock adiabatics, is delivered, and the formulas of calculating sound velocity along isentropic and isothermal compression, as well as the Hugoniot curves, are presented. The Hugoniot sound velocities of aluminum and tungsten are calculated. The calculated results are in good accord with the experimental results.