A concentration depletion is developed nearby a capillary wall from the result of flow-induced radial migration to the axis region of capillary incorporating with the chain extension, The velocity enhancement factor can be defined quantifying the migration of polymers. For the experimental observation of the radial migration, the capillary hydrodynamic fractionation (CHDF) system has been adopted as a probe on the microcapillary flow of water-soluble flexible polymers. As a practical implication, the migration phenomena may lead to apply this system due to the possible alteration of the elution characteristics. In order to verify the experimental results more accurately, a model has been provided based on the diffusion equation and the conformation-dependent friction involving a radial dependence of hydrodynamic force on the dumbbell extension, For the nonionic polyacrylamide, the experimental behavior of velocity enhancement was shown to be in accordance with the present model within the somewhat increased We, In case of the anionic polyelectrolyte with 30% hydrolyzed polyacrylamide, the increasing slopes of velocity enhancement are different with the eluant ionic strength. Note that the experimental data allow us to consider an enhanced migration due to the long-ranged repulsive force between capillary wall and polymer.