In traditional indentation test methods for obtaining Norton's law of creep materials, an empirical correlation formula represents the relationship between the indentation strain rate and the uniaxial reference strain rate or indentation displacement rate. This study proposes an equivalent method for representative volume elements (RVE) of creep materials from a complex stress state to a simple stress state. Considering Norton's law as a constitutive relationship based on the equivalent method of stress state, a semi-analytical model describing the creep displacement vs. time relationship of flat cylindrical indentation (flat indentation) and a method for determining the parameters of the model were established under constant load conditions in this investigation. The finite element analysis (FEA), creep test results of zinc alloy ZA27, and results in the current literature were used to verify the semi-analytical creep model. The results showed that Norton's law and the displacement rate predicted by different indentation creep models are relatively close, and the partial results predicted by the new model are slightly better than those obtained by methods reported in the literature.