Abstract: To solve the problems of slow convergence, of the low accuracy and of easily falling into local optimal solution of the standard firefly algorithm, an improved firefly algorithm with parameter adaptive strategy is proposed, and a finite element model updating method based on this improved firefly algorithm is established. An alternate generation random attraction factor is introduced to expand a search path, thus the ergodicity of the standard algorithm is improved, and result will no longer trapped in the local optimum. Furthermore, the adaptive step size factor is developed to reduce the random search range gradually with iteration in the updating process, so as to speed the convergence. The calculation results of single peak and multi peak test functions show that the improved algorithm significantly improves the convergence rate and accuracy. The numerical example of simply supported beam and the finite element model modification results of a real continuous rigid frame bridge show that: the maximum error of parameters of simply supported beam is reduced from 66.7% to 1.08% after modification, and the maximum frequency error of the continuous rigid frame bridge is reduced from 14.47% to 3.25%. The proposed method has good updating accuracy and is suitable for finite element model modification of large and complex structures.