The code of three-dimensional fluid dynamical analysis of convection in a liquid column of diffusion sample in a cylindrical container was developed. Temperature reaches a steady value quickly than the velocity. Only slight convection appeared in the present simulation condition (short time). However, with the progress of diffusion, the convection may be considered to occur depending on the experimental condition. In future, its detailed comparison with experiments is to be presented in the case of laboratory experiments under lG condition for liquid Ag+(0.95)Ag(0.05)Au.