In order to model the creep aging process of Al-Zn-Mg-Cu aluminum alloy using common temperature-related two-stage aging, a constitutive framework is proposed considering the creep strain and yield strength. The material parameters involved in the model were estimated using a simple fitting method from the experimental data. With a simple expression, this model was capable of handling stress relaxation, hardening response, and variable aging temperature in the creep aging process. It could also be implemented using finite element analysis software to simulate the creep strain, yield strength, and springback of the component. The modeling results were consistent with the creep strain curves measured under different applied stresses. The numerical simulations were compared with the applied experimental data and excellent consistency was observed between them.