When the magnetoelectric velocity sensor is used to test the vibration of the top cover, distortion is easy to occur due to the inherent characteristics of the sensor and the test conditions, and the data can not truly and effectively reflect the operation state of the water turbine top cover. The correlation among excitation force, vibration and strain was clarified through vibration theoretical analysis and stress calculation of top cover structure. Using finite element structural analysis to determine the weak position of the rigidity and strength of the top cover, the dynamic strain value based on this position was proposed as an indicator parameter for evaluating the operation status of the hydraulic turbine top cover. Based on the vibration value and dynamic strain value in the stable operation area, a mapping relationship between strain and vibration was established to solve the problem of inaccurate vibration measurement of the top cover. Taking a power plant unit as an example, the feasibility of the proposed method was verified.