The creep behavior at 130~240 MPa /973~1023 K of Sanicro25 steel for ultra-supercritical power plants were investigated by OM, SEM and TEM. The results showed that the minimum creep rate increases with the increasing temperature and applied stress. Based on the characteristics of the minimum creep rate, the stress exponents of 7.6~8.2 and the apparent activation energy of 496.7~531.8 kJ/mol can be acquired for the creep process. Nano-scale Cu-rich phase and MX phase precipitated in the matrix imped the dislocation motion, thus resulted in the emerging of creep threshold stress. The creep threshold stresses can be estimated by the linear extrapolation method, and which decrease with the increase in temperature. By invoking the concept of the threshold stresses to modify the constitutive equation, $\dot{\varepsilon}_{\min }=A_{2}\left[\left(\sigma-\sigma_{\mathrm{th}}\right) / G\right]^{n} \exp (-Q / R T)$, the normalization of the minimum creep rate can be acquired at various temperatures; Meanwhile, the true stress exponent (n=5) and the true apparent activation energy (Q=286.6kJ/mol approximately equal to the γ-Fe self-diffusion activation energy) can be identified. The creep rate-controlling mechanism was determined to be dislocation climbing mechanism assisted by lattice self-diffusion.