A novel calculation method has been developed from the physical operating process of exploding foil initiators (EFIs) for predicting its sensitivity. The absorbed energy of metal foil bridge during electrical explosion was calculated using a dynamic resistivity model. The electrical energy is proportional converted into the flyer motion because of the effects of light, heat, and electromagnetic wave. The flyer velocity of EFIs was calculated by the one-dimensional Lagrange hydrodynamic model with the help of the correction factor. Depending on a developed ignition and growth model, the shock initiation by the flyer impact process was simulated for the built-up detonation characterization. The current, voltage, and flyer velocity were measured in order to validate the accuracy of the calculating models. The threshold flyer velocity (2.85 km s(-1)) for initiation of HNS-IV explosive pellet was determined by the shock initiation modeling. The threshold firing voltages were calculated from the electrical explosion and flyer motion modeling. The calculated sensitivities of EFIs with 0.2 mm barrel length are easily converged to experimental ones, yet that with the 0.4 mm barrel length has an evident error. The breakage and ablation of the flyer have significant influences on the shock initiation at a longer barrel length.