The force-distance (F-D) curve in AFM analysis is a useful technique in the field of biophysics and surface science for measuring the physical/chemical properties of a substrate. Herein, the dependence of Vz on the F-D curve has been described via a theoretical investigation confirmed with measured data. The results show the attractive force was gradually reduced above a Vz of 5 μm/s by increasing the external repulsive force loaded onto the cantilever. To obtain a non-distorted F-D curve, one of two methods should be used: to analyze F-D curve under Vz of 1 μm/s or use of a short/stiff cantilever.