Based on flow chamber technique and using carrier microspheres as force magnifiers, an investigation of the interaction force between surface immobilized ligand and objective molecule was carried out. Human immunoglobulin G (IgG) and goat anti-human IgG (anti-IgG) were employed as model ligand and model objective molecule respectively. The parameters of the flow field were designed based on Plane Poiseuille Flow and the design was validated by a numerical simulation. Using bovine serum albumin (BSA) as negative control, it was concluded that the adhesion force between the microspheres and the chip surface came from the specific interaction between the ligand and the objective molecule. And this conclusion was confirmed by an anti-IgG deactivation comparison. It was found that the adhesion force between the spheres and the chip surface was affected by the ligand surface concentration. The wall shear rate at which 95% microspheres were removed from the chip surface was set as the critical value, and the relationship between the critical shear rate and the ligand surface concentration was obtained. A mechanical analysis model considering both the ligand surface concentration and the difference of molecular bonds' position was proposed, which finally gave the result that the average interaction force between a single pair of ligand and objective molecule was about 342pN.