Abstract: By the linearization method, the mathematic model of point reactor can be simplified. The simplified point reactor model could be further converted to the transfer function with the Laplace transfer tool. Until now, the point reactor transfer function is still used as the basic means for researching the nuclear reactor control system and the relative engineering items. However, through the analysis, it is found that the linearizd point reactor model based on the hypothesis that reactivity is zero when reactor is at the stable state has its own problems. This paper gives the concise analysis of the problems. The analysis method is the combination of theory and experiment. Theoretically, the focus is to compare the time domain results and the frequency domain results by means of the system dynamics principles. Experimentally, based on the engineering parameters, the focus is to compare the time domain computer simulation results and the frequency domain computer simulation results. Through the comparison analysis, the problems are exposed clearly. The paper gives the model modification access for the problems accordingly.