A structural system can be functionally experience by structural and its corresponding modal parameters. Likewise, the parameters are the basis of describing a system. The way of model updating structural system parameters has been developed for years; most of studies are analyzed under a presupposition that mode shape is already known. Therefore, the errors and disadvantages are embedded in those studies. Our thesis is designed without measuring mode shape and provides an alternative way to acquire mode shape. Furthermore, the study is accompanied by a suitable way of revising structural system parameter in order to enhance the accuracy of the result. The method is based on two strategies: 1. Concentrating stuffiness matrix and mass matrix by Iterative method for dynamic condensation of structural matrices. 2. Improving the accuracy when measuring mode shape by setting modal parameters in a way of combining frequency information and Genetic Algorithms. Respectively, one reduces the amount of parameters and advances the search in high intensity; and the other, accompanied with the property of Iterative method for dynamic condensation of structural matrices and mode shape from the previous strategy, revises structural parameters by Cross-model cross-mode method for model updating. In conclusion, the effective value of revising structural system parameter can be executed by only a decisive frequency of the whole structure. This solves the disadvantages in traditional studies of measuring mode shape , and fulfills the purpose of revising structural system parameters.