An accurate stress estimation for creep evaluation is essential for the long-term safe operation of components at elevated temperature. In general, the section-dependent parameter Kt is defined in elastic analysis routine to account for the reduction in extreme fiber bending stress due to the effect of creep action. A constant value is provided for each cross section in ASME III-5 code, but this may induce underestimation or overestimation of the representative stress of the component due to the relevance of parameter Kt to many factors. Therefore, it is essential to re-examine the validity of the parameter Kt in ASME III-5 code for an adequate creep evaluation. In this work, numerical analyses on beam models with a rectangular section are conducted to calculate parameter Kt, and effects of related factors to the parameter Kt are included. The results reveal that the parameter Kt is closely related to the design life, loading level, operation temperature, and loading combinations. It can be higher than that for the pure bending moment (or tensile loading) with the introduction of the tensile loading (or the bending moment). Meanwhile, the parameter Kt may be higher than the value (i.e., 1.25) in ASME III-5 code for a longer design life, a higher loading level, and a higher operation temperature, inducing an overestimation of the representative stress. On the contrary, a smaller value than 1.25 can be found, inducing an underestimation of the representative stress for creep evaluations.