Abstract: In order to obtain the basic data for determining the parameters of the JWL equation of state of unreacted PBXC10, an approach which was based on the pressure histories at different Lagrange positions in a PBXC10 explosive obtained by the shock initiation experiment was proposed to obtain the unreacted shock Hugoniot relationship for the explosive. In the meantime, the explosive in the front of the shock wave was nonreactive and the momentum conservation before and after the shock wave was utilized, so that the shock Hugoniot relation for the unreacted PBXC10 explosive was obtained in this paper. The von Neumann spike pressure of the PBXC10 explosive was given after extrapolating this relation to the detonation velocity to yield. It is found that the ratio of this spike pressure to the Chapman-Jouguet pressure of the PBXC10 is in a reasonable range.