Abstract: With the development of key engineering projects such as aviation and nuclear power, the demand for a method of measuring material toughness using small specimens has greatly increased recently. A test method using a C-ring specimen with small dimensions to investigate fatigue crack propagation behavior is proposed. The C-ring specimen dimension and its loading fixture are designed, and a compliance formula and expression of stress intensity factor of the small specimen are proposed based on finite element analysis. For 26 NiCrMoV11-5 rotor steel, the fatigue crack propagation behavior of the material is investigated, and validity of the new method is discussed.