We modeled the bending deformation of the subducting plate at the southern Mariana using a 3-D elastic plate flexural model. Intraplate stresses were investigated, with the along-strike variable boundary loadings. In order to match the observed plate geometry, boundary vertical loading near the Challenger Deep had to be set twice of that in the region further east within our study area. By comparing results between 2-D and 3-D models, we found that the difference on estimating plate stress can exceed 20% when there is an along-strike variation in plate bending. Finally, we found that the sharp lateral variation in the σ and the σ corresponded to an outer-rise earthquake cluster at the southern Mariana subduction zone, indicating that along-strike variation in σ and σ may be a significant mechanism to cause non-uniform distribution of outer-rise earthquakes.