In this paper, we have proposed a new method for identifying specified parameters in linear systems. The method is based on Youla-parameterization, which is derived by pulling out the deviations of specified parameters to the references. The resultant parameterization takes a form of linear fractional transformation (LFT) and has an arbitrariness on the stable factors of parameterizing. We can utilize the arbitrariness to enhance the accuracy of estimating specified parameters because the stable factorizing in the parameterization means introducing a filter for suppressing the effect of observation noises. Two examples are given for illustrating the effectiveness and for showing the possibility of applying the method to fault diagnosis.