In order to find the global optimal solution and obtain more exactable finite element model, model updating is carried out by using multi-island genetic algorithm (MIGA). Taking the residual error of the numerical and field-measured structure response as objective optimization function, an optimal mathematical model is set up, which refers to the dynamic response of bridge structure, element elasticity modulus, density and dimension of the element cross section. The MIGA is adopted as optimization policy. Simulation example of a bridge model is used to demonstrate the method. The result shows that the proposed method works well and the updated model represents the dynamic property of the structure availably, which demonstrates its feasibility and validity.