In tap test on the honeycomb sandwich structures, the contact time of the tapping head changes with the flow sizes and the plates. To quantitively show these relationships, a mechanical model describing the tapping head movement was given. The equation of the contact time varying with the flow diameter and the plate tension was derived. The contact time variations under different tension parameters were given and compared with the experiment data. The result shows, by using suitable tension parameters, the contact time given by the mechanical model agrees with the experiment data. The model can be used to calculate the contact time and analysis its variation. For flows on a same plate, the contact time increases with the flow diameters. For flows with same diameter and on plates with same material, the contact time decreases with the plate thicknesses. For flows with same diameter and on plates with same thickness, the contact time on a FRP plate is shorter than that on an Al plate.