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The blanket module of nuclear fusion reactor is proposed to be made of reduced activation ferritic martensitic (RAFM) steel. Thus, in order to prevent the unprecedented failure, the creep response of RAFM steel must be studied meticulously. In that direction, physical based creep curve modeling is one of the available choices to obtain the insights about the substructural evolution during the creep deformation, hence enabling to enlighten about material weakening mechanisms. In this paper, experimental creep curves of RAFM steel at varying conditions are simulated employing an improved dislocation density reliant physical model. The microstructure based internal variables are considered for addressing the mechanisms such as hardening, recovery, coarsening of precipitates and creep cavitation. All the simulated creep curves are found to be in reasonable agreement with the experimental creep curves. Furthermore, the evolution of involved eighteen parameters, i.e., dislocation glide velocity, climb velocity, internal stress, climb stress, effective stress, mobile dislocation density, dipole dislocation density, boundary dislocation density, subgrain radius, boundary pressure, boundary dislocation spacing, subgrain mobility and dipole capture spacing is demonstrated and discussed thoroughly.