In this study, based on the rod tensile model, a conversion relationship between three-point bending specimen with fixed constraints (TPBSF) and uniaxial creep data in the large deformation stage is defined by the reference stress method. Using finite element method, conversion coefficients are determined. Then it is verified by the creep test data of A7N01 at 350 °C (Zhuang, F. K., 2014, “Research on Creep Test Method of Small Specimen Based on Beam Bending Theory,” Ph.D. thesis, East China University of Science and Technology, Shanghai, China). The results show that creep stress exponent n is the same, but creep constant B obtained by rod tensile model is much closer to uniaxial creep than beam bending model. Finally, effects of geometric parameters and friction on conversion coefficients are investigated. On this basis, the specimen cross section aspect ratio greater than 1 and the indenter radius larger than 1 mm are recommended to minimize the influence of TPBSF geometric parameters on conversion coefficients. The influence of friction on conversion coefficients can be negligible.