Abstract: The seismic response of hydraulic turbines underwatermedium is the typical coupled vibration of liquid-elastic body. To begin with, this paper briefly introduces the theory background and computation method about dynamic behavior of turbines in water, then focuses on discussing the dynamic governing equations of turbine-water system in consideration of the influence of 3 dimensional coupled vibration of liquid-turbine. The time-history analysis is adopted to resolve the equations. Finally, an example of a practical case is given, with the computational result compared against the result obtained without considering the influence of water medium.