A phage display library is a powerful tool for screening ligands such as antibodies and peptides that specifically recognize a target. In this study, we established a kinetic model describing the affinity selection process of phage display libraries and verified the model experimentally. Desorption of target molecules from a solid phase and orientation of the epitopes of adsorbed target molecules are taken into account in this model. The ratio of the effective antigen density to the total antigen density was estimated to be 0.0127(+/-)0.0018 when bovine pancreatic ribonuclease A (RNase A) adsorbed on polystyrene beads was recognized by an anti-RNase A single-chain Fv phage antibody. The model can faithfully describe the recovery of the phage antibody in a round of biopanning based on the effective concentration of RNase A on the beads, the desorption rate constant of RNase A from the beads, the dissociation constant and dissociation rate constant of the phage antibody from RNase A, and the time for blocking, equilibrium and washing in the biopanning process. A recommended biopanning protocol based on the model is also described.