An appropriate evacuation is necessary to reduce damages due to flood disaster. However there are little information for underwater walking in evacuation. In this study, we conducted the laboratory experiments for walking speed in water under various conditions. For this, we set totally 49 cases for water depth and velocity, and several surrounding environment for which kinds of shoes, turbidity of water and light conditions are changed. The results indicated that the inverse correlations between walking speed and hydraulic parameters were obtained. The walking speed with the environmental conditions were 50 -60 % of it without the environmental conditions. Critical conditions of underwater walking were quantitatively evaluated under various hydraulic and environmental conditions.