Abstract: Integrant modal data are used to update a five-layer steel frame.The comparisons between the efficiencies and precisions of the GeneticAlgorithm (GA), Particle Swarm Optimization Algorithm (PSO) and GA-PSO inthe model updating processes show that all the four modal frequencies andmodal shapes of the updated model can approach the target values with in varyingdegrees, which proves that these methods can all efficiently update themodel. In particular, GA-PSO algorithm uses GA to efficiently search forthe global-optical solution at an early stage, and uses PSO to intensivelysearch for the local-optimal solution at a later stage. Comparing with thePSO and GA, GA-PSO algorithm enjoys higher updating efficiency and precision.