The modal experiments a single pile and a pier were implemented. In order to synthesize the two parts of the experiment results into a whole and minimize the destruction, the sensors were installed on the pile in the experiment. A simple modal synthesis method has been derived. The first is the symmetry of the model, the second is the theory of frequency response characteristics of composite systems, and the third is structural displacement harmonized condition. This method realizes the combination of the pile -pier modal. At the same time, the finite element calculation results are consistent with the experiment results, which validates the feasibility of the method proposed.