Impact on tritium behavior in the atmosphere was numerically analyzed and the tritium deposition coefficient onto water surface was measured by an experiment. Measured deposition coefficients were observed to vary with the mixing of water. It was shown by numerical analysis that when deposition coefficient was grater than 0.5, it could be expected that about 70 % of released tritium would be absorbed by water when release point was set on the sea and that when it was 0.15, about 40% of tritium would be absorbed.