Abstract: A baseline model is usually used in the safety appraisal and strengthening analysis of bridges on service, which is of defects. In this paper a multistage modal updating method, which caters to actual bridge inspecting experience, is presented based on traditional structural parameter estimation by optimization theory. Three-step parameterization is applied in it: parameters to be update are ranked according to their sensitivity to error index EI and the finite element model is updated stage by stage. The modal updating efficiency and effect are compared between different updating parameter ensembles and different updating methods and the updated finite element model is utilized in carrying capacity of bridge on service. The results show that multistage modal updating displays a higher efficiency and a better effect than straight modal updating and the updated model is able to realize systematically the specific safety appraisal of bridges on service.