Abstract: Torsional stiffness is one of the important indicators to measure the overall performance of wind power couplings. This paper first introduces the achievements of the stiffness analysis and diaphragm stress calculation of metal diaphragm coupling. On this basis, relevant mechanical theories are applied to solve the problem of torsional stiffness calculation for glass fiber reinforced plastic tubes, and a complete mathematical model for the theoretical calculation of torsional stiffness of wind power couplings is established. Then, by using the working principle of the connecting rod mechanism, the test device of torsion stiffness measurement is designed, and the measurement principle is introduced. By measuring the displacement indirectly, the relationship between the output force of the piston rod and the input torque of the wind power coupling is analyzed in detail, and the mathematical model of torsion stiffness measurement is established. Finally, the correctness of these two mathematical models can provide an important reference for the calculation and measurement of the torsional stiffness of large coupling.