For atomic force microscopy (AFM), fast scanning usually results in low imaging resolution, which leads to inaccurate sample topography reconstruction. Based on the analysis for the experimental step-response of AFM, a practical dynamic imaging method is proposed in this article to enhance measurement performance under fast scanning speed. Specifically, the experimental step-response is employed to obtain the transient displacement of the piezo-actuator in the Z-axis, which is then utilized, together with the control error, to calculate the topography of the detected sample surface. As no model is required to enable this algorithm, it presents such advantages as easy implementation and reliable imaging results. Some experimental results are included to demonstrate the superior performance of the proposed imaging method.