Earthquake analysis of fluid structure coupled system has been studied in the present paper. The structure that has been considered here is a concrete gravity dam, and the fluid is the reservoir water adjacent to the upstream face of that dam. Under seismic disturbances, the concrete dam moves into and away from the reservoir water; as a result of it, in addition to the hydrostatic pressure, water exerts hydrodynamic pressure on the upstream face of the dam. The mutual interaction between the dam and the reservoir is studied here through direct coupling approach using standard finite element method. Displacement based and pressure based finite element formulation is considered to model the dam and reservoir domains, respectively. The interaction algorithm implemented here has been validated with the existing literatures. Displacement and stress time histories are obtained for the coupled system for the earthquake loading. Comparison of the time history responses of the dam with empty reservoir and full reservoir condition justifies the significance of the consideration of coupling of the fluid and structure domain in the earthquake analysis of a concrete gravity dam.