To obtain optimal field emission (FE) properties, it is important to evaluate FE parameters including the electron emission site α and the field enhancement factor β. However, it is difficult to evaluate α quantitatively because the emitting electrons cannot be observed directly. The authors have aimed to analyze this site using an original architecture with a computation system tool based on the surface charge method, and a three-dimensional model has been employed to calculate FE properties with high accuracy. In this study, to analyze α for determining FE properties, each carbon nanofiber (CNF) model separated by Cr islands which include the minimum area for calculating electric fields by the surface charge method was constructed on the surface of a Ni catalyst. The FE current was simulated with a Fowler-Nordheim formula using the calculated electric fields, followed by a simulation performed using all CNFs on a field emitter cathode. The electron emission site α was determined by comparing the simulation and experimental results of the FE current. It was found that α depends on the morphology of the CNF bundles, and a close quantitative correspondence between the experimental and the computation results of FE properties was obtained. In summary, a method of analyzing FE properties was established using an original architecture, making it possible to predict FE properties with a computational tool based on the surface charge method.