The primary objective of this study is to develop a quantitative model to predict the effects of materials, environment and mechanics such as loading configuration on environmentally-assisted cracking (EAC) of stainless steels in high-temperature water. It has basically been accepted that crack propagation in oxygenated high temperature water is controlled by a slip-dissolution and/or deformation-oxidation mechanism. According to this mechanism, the crack-tip strain rate is an extremely important mechanical parameter for determining the crack growth rates. Based upon a formulation obtained by combining Faraday’s equation with an elastic plastic analysis of the strain singularity at a growing crack-tip in work hardening materials, a theoretical formulation of crack-tip strain rate has been derived for plane strain and plane stress conditions. The FEM analysis for 3D crack growth can be compared to the theoretical 2D analysis. In this paper, we first make a CCP (Center Crack Plane) model, and performed a 3-dimensional Finite Element Analysis (3D-FEA) to evaluate the crack-tip stain rate paying attention to the element mesh size and to the loading history. After optimization these parameters, the calculated crack-tip strain distribution, including its logarithmic singularity, was founded to agree well with the theoretical distribution. The significance of the crack-tip strain rate upon the crack-tip strain distribution and crack growth rate was demonstrated. The specimen size effects on crack growth rates were discussed from this point of crack-tip strain distribution. Finally, we focused on the importance of crack-tip strain rate as a unique mechanical parameter that controls the crack growth rate.