A new material parameter &bgr;:&bgr; = (&rgr;0 − &rgr;00 pH/PH′)/&rgr;0&rgr;00 (1 − PH/PH′), where &rgr; is density and subscript 0 and 00 represent different initial density, andPHandPH′represent Hugoniot pressure of &rgr;0and &rgr;00which compressed to the same density &rgr;, was find out to keep in constant along Hugoniot. For metal&bgr;metal=1.217&rgr;0−0.884, where &rgr;0is the ideal crystal density. By using of &bgr;, Hugoniot data of different initial density samples can be simply converted by:PH = PH′ &rgr;0 (&bgr;&rgr;00 − 1)/&rgr;00 (&bgr;&rgr;0 − 1), and a new empirical Equation to express Hugoniot State was obtained:pHVn = p0V0n, wherenis constant. The properties and limitation of this empirical material parameter to be constant with variations of pressure and porosity were discussed. © 2004 American Institute of Physics