In the present study, the authors proposed a numerical analysis procedure to evaluate both material flow and tool strength due to friction stir welding (FSW) using particle method and finite element method (FEM).In the proposed evaluation method, material flow during FSW is simulated by the particle method. And then, the calculated pressure distribution on the tool surface is interpolated in the FEM analysis for the evaluation of tool strength. The proposed method was applied to the investigation of the influence of the traveling and rotation speed on the maximum temperature in the welded material. Stresses on the tool surface was also investigated using the proposed method. The result indicated that the traveling speed has large effect on surface stress while the effect of rotation speed on surface stress is small.