Abstract: In order to study the applicability and accuracy of a modal work method in calculating hydraulic damping of rotating machines, the test data of the rotating disc damping measurement system were used to evaluate the modal working, validating the hydraulic damping method. The results show that the hydraulic damping value of the disc decreases with the increase of rotational speed. The influence of rotation effect must be taken into account when the modal working method is used to calculate the hydraulic damping value. If the modal results under static conditions are directly used, the trend will be completely contrary to the test results. Considering the condition of rotation, the calculation accuracy can be improved, but there is an over-prediction problem in the whole process. So, the accuracy of this method will still need to be improved in predicting the damping characteristics of rotating structures.