The aim of this study is a characterization of boiling hydrogen flow in horizontal circular pipe flow. The most important parameters for boiling flow are a void fraction and flow quality. Although the void fraction is measurable in some way, there is no established method for cryogenic fluid. The authors developed a capacitive void fraction sensor and applied it for boiling hydrogen flow experimental facility. The correlations between the void fraction and flow qualities are investigated by comparing the previously proposed models. The conversion model of the combination of Sekoguchi simple model and the Steiner model agrees very well with the experimental result.