By analyzing the application difficulties of parameter estimation， the parameter estimation feasibility of power system is discussed. The concept of dominant parameter and non-dominant parameter is proposed with the help of approximate analysis by using the linear model of power system. Therefore the behavior of parameter estimation practice can be explained and the inference for the software running mode of parameter estimation can be drawn from the linear model of power system. Employing the fact that the non-dominant parameter is susceptible to measurement noise， a method of identifying the non-dominant parameter based on the noise sensitivity experiments is presented. Simulation results of an IEEE sample power system are given to verify the viewpoint proposed that the non-dominant parameter should be wiped out in the parameter estimation.