Mechanical properties of N15 solid propellant under different confining pressures were obtained by using the confining pressure test system. Result showed that the initial modulus of the propellant did not change with the confining pressure

but the maximum tensile strength

rupture strength

the maximum elongation and elongation at break increased with the increase of confining pressure; combined with propellant’s mesoscopic structure and cross section analysis

the mechanical mechanism of confining pressure effect on the propellant was revealed preliminarily; as a result of the existence of confining pressure

the particle dewetting inside the propellant was reduced

the holes’ propagation delayed due to the pressure

and its crack extension and germination was inhibited

which proved that the confining pressure had strengthening effect for propellant; according to the elastic-viscoelastic correspondence principle

a constitutive model considering the confining pressure effect was established for N15 propellant. The results showed that accuracy of the constitutive model was good

and it can describe the influence of confining pressure on the mechanical properties of N15 propellant accurately.