Abstract: A substructure isolation method is proposed to update a local substructure by utilizing the impulse response at the corresponding substructural location of the whole structure, which is significant when only a local part of the structure is interested. Firstly support pressures needed to apply on the substructural boundary are estimated via impulse response at the location of a substructure, in order to construct the impulse response of an Isolated Substructure. Then Eigensystem Realization Algorithm (ERA) is used to identify the modal parameters of the constructed impulse response, thereby the local substructure is updated through the model identification and model updating of an Isolated Substructure, an individual structure by applying numerical support on the substructural boundary. It contains fewer elements and can be updated easier with high computational efficiency, as well as improved computational precision since that the influence from the other parts of structure is eliminated. A numerical example of a plane truss is given and validates that a substructure could be updated successfully by using the displacement, velocity and acceleration impulse response at the substructural location respectively even with 10% Gauss noise.