In the paper, an apprcach linking BEM and dynamic measurement is presented to identify the boundary conditions of a structure. In deriving the boundary integral equation, an approximate fundamental solution is employed, which consists of the Tchebychev orthognal polinomial series. A thin plate structure is studied and the computer simulation is carried out toestimate the elastic support stiffness of arectangular plate. The simulation result verifies the effectiveness and the reliability of the method offered.