Abstract: The 35CrMo steel of volute bolt of hydropower unit was subjected to axial tensile by using tensile testing machine and ultrasonic stress detector, and the stress value and the corresponding ultrasonic transverse wave and longitudinal wave propagation time were measured in the process of tensile, so as to obtain the sound-hour ratio of ultrasonic transverse wave and longitudinal wave, that is, the wave velocity ratio of ultrasonic longitudinal wave and transverse wave. The quantitative relationship between elastic stress and ultrasonic time ratio of shear wave and longitudinal wave is established to provide a basis for real-time determination of bolt elastic stress by ultrasonic wave. The results show that the axial elastic stress of 35CrMo steel is within the elastic deformation range of steel, and there is a linear relationship between the acoustic time ratio of shear wave to longitudinal wave and the elastic stress.Through the error analysis of the model, the results show that the error between the stress value and the actual stress value measured by ultrasonic shear wave and longitudinal wave is between 0. 04 and 2. 08%, and the error meets the engineering requirements.