The subject of whether or not physical entanglement networks contribute to the elastic mo-dulus of polymer is still at issue．According to the Flory’s swelling theory and theory of rub-ber elasticky，the characterization of chemical crosslinking networks and physical entanglement networks of radiation crosslinked cis-1，4-polybutadiene(cis-PB) as well as influence of ne tworks structure on the mechnical properties were investigated in this paper．Resuks display that the density of physical entanglement networks is much higher than that of chemical cros-slinking networks．With the increasing of radiation dose，the density of chemical crosslin-king is increased，but the number of entanglement is decreased．The relations of crosslinking/entanglement density and constants C1 and C2 of Mooney-Rivlin equation were explored．Results show that the constant C1 is attributed tO chemical crosslinking networks；while the constant C2 is attributed to physical entanglement networks．The physical entanglement net-works mainly contribute to the initial elastic modulus Go of crosslinked polymer for small strain；while the chemical crosslinking networks chiefly contribute to the break strength of crosslinked polymer for the large strain．