The effect of different water loads and different action modes on the high concrete dam’s displacement component was studied. Some conclusions were obtained：①When the foundation range is increased, water load on the foundation is to be considered whether it is an area load or a seepage volume load, the horizontal displacement of the referenced base point increases. However, the value measured by a reversed pendulum fixed at the rock foundation is often regarded to be absolute displacement. The above practice is regarded as to be limitative when the water load on the dam foundation is taken into account. ②It is proposed that the displacement of the referenced base point should be considered in order to obtain accurate inversion value of parameters. The parameter back analysis needs to adopt the relative displacement value of dam crest and base point calculated by the infinite element numerical computation, together with the measured component of water pressure from displacement.