Abstract: A three-dimensional computational fluid dynamic code CYCAS was developed for hydrogen safety analysis. The code solved three-dimensional, compressible and unsteady Navier-Stokes equations by the numerical method of implicit continuous Eulerian-arbitrary Lagrangian Eulerian. Multi-component mass conservation equations were solved to describe the diffusion and mixing phenomenon. A homogeneous equilibrium model was applied to model the phase change of water vapor in the fluid flow. For the phase change near the wall, the Chilton-Colburn empirical analogy was used. Algebraic and k-ε turbulence models were employed to model the turbulent flow. The turbulent jet –experiment- HYJET and the international standard problem ISP23 were simulated and analyzed for CYCAS validation. The computational results agree well with the experimental data.