To reveal the relationship between the evolutions of polymer chains within the NEPE propellant matrix and the hyperelastic mechanical behavior， a multiscale approach was adopted to investigate the evolution behavior and characterization model of polymer chains under different deformation states. Firstly， based on the microscopic models of components such as matrix adhesives， curing agents， and plasticizers， a dynamic model describing the evolution of cross-linked and free chain configurations under complex deformation states was developed through molecular dynamics simulation of the matrix system Subsequently， the free energy contributed bycrosslinked and free chains was quantitatively characterized based on statistical mechanics， and a hyperelastic constitutive model considering the cross-linking and entanglement effects was established. Finally， the developed constitutive model was validated by using the quasi-static tensile experimental data of NEPE propellant matrix samples. Compared with the classical Arruda-Boyce model， the constitutive parameters in the present model have real physical significances and can be obtained by experimental methods， which enables the present model to better predict the hyperelastic behavior of the propellant matrix under different deformation states， and thus provide model for the regulation of mechanical properties and component optimization of propellant matrix.