It is planned to use hydrogen extensively as a source of clean energy in the next century. When using hydrogen it is necessary to consider safety because of its potential hazards such as explosions. The data obtained from laboratory-scale experiments have been sufficient to confirm the safety of small-scale uses of hydrogen in the past. However, computer simulation of the behavior of leaked hydrogen will play an important role in confirming the safety of extensive uses of hydrogen in future because of the large quantities involved and the presense of hydrogen in a phase other than the gas phase. In suppport of the JAPAN MITI/NEDO World Energy Network(WE-NET)project, MHI has been tasked by Institute of the Applied Energy (IAE) to evaluate the accident scenarios of the leakage of liquid hydrogen. The formation and dispersion of flammable vapor clouds resulting from massive liquid hydrogen (LH(2)) spills has not yet been simulated because the multi-phase and multi-component nature of the vapor cloud presents one of the most difficult problems for computer simulated fluid dynamics. Since we have developed the multi-phase hydrodynamics analysis code (CHAMPAGNE)([1]), we applied the code to simulate the formation and dispersion of hydrogen vapor clouds([2]). It was found through these preliminary calculations that the mass flux evapolated from the leaked liquid hydrogen exerted a serious influence upon the spreading of the hydrogen vapor clouds. In the present paper, therefore, we have developed the calculation model of the evaporation rate and incorporated the model into the CHAMPAGNE code in order to calculate the behavior of the hydrogen during the experiment in which 5100-liter quasi-instantaneous LH(2) spills were performed at the NASA White Sands Test Station. Though we can use the experimental data for evaporation of liquid hydrogen obtained in only small scale under the stagnant condition, we have improved the evaporation model by comparing calculated results with the data.