Abstract: In this paper, with theoretical modeling and experimental correlation, a semi-empirical model which can predict the hydrogen distribution characteristics has been proposed, based on the dominant factors of interaction among the inertial force, viscous force and buoyancy under the injection of both steam and hydrogen. The rationality of the model is verified by comparing with the experimental data under the injection of medium and high content of steam. All the theoretical work can provide extra support to further develop the hydrogen distribution model coupled with condensation effect within the containment in the future. Moreover, its application in the study of the typical hydrogen behavior on small-scaled containment model of CAP1400 demonstrates that there may be reservoir of light gas, gradient layers and stagnation region along the vertical direction, which is in line with the findings by international benchmark tests (ISP47).