A theoretical and experimental investigation of the force-distance relation in the case between a pyramidal tip and a cell is presented. The shape of the tip in use consists of a truncated pyramid covered by a spherical cap. The interaction force is computed the total interaction between macroscopic bodies. The experimental method is depicted in detail. The experimental results are comparison with the theory. The mechanical properties of the cell can be determined accurately and spatially well resolved from interaction force of tip-cell in AFM.