We are studying a new analysis method for transient responses by using the digital filter. This paper demonstrates some time-frequency analysis results of responses based on typical differential equations. First, we present the results for the linear free and forced vibration responses of one degree-of-freedom system. Then we consider the responses based on Duffing's equation and it is shown that the dominant frequency change of the responses can be visualized in the time-frequency analysis results. And the responses based on Van del Pol and Mathieu equations are analyzed to understand the several dominant frequencies. Finally, we apply the time-frequency analysis to the data of car bumping and it is shown that the phenomena may be described by the Duffing's equation.