Abstract: For the complex modal analysis of the soil-bedrock model of two-dimensional basin site, it is difficult to select several local soil modes from the numerous modes. Therefore, the modified local modal mass ratio is proposed to form the complex-mode-based identification method for the dynamic characteristics of soil layer on a two-dimensional basin site. The method uses the state-space method to calculate the complex modes of the soil-bedrock finite element model including the influence of radiation damping. Then, the local modes of the soil are identified by the modified local modal mass ratio. Taking the semi-elliptic and rectangular basin sites as examples, the difference of dynamic characteristics obtained from different calculation models of basin sites is discussed, and the influence of soil layer geometry, of width-depth ratio and, of impedance ratio on the number of local modes is studied. The numerical results show that the modified local modal mass ratio can effectively identify the local modes of soil in the basin site. The number of local modes increases with the increase of a basin width-depth ratio and decreases with the increase of an impedance ratio. When the impedance ratio between soil and bedrock in the basin site is greater than 0.4, obvious local modes of a soil layer would not be observed.