In this article, the Elasto-plastic analysis of thick walled FG tanks subjected to internal pressure is elaborated. Today, thick walled tanks containing liquids with high pressure are used in the chemical industries. The high internal pressure causes part of the thickness of reservoir to yield; therefore, we need the Elasto-plastic analysis. In this study, Elasto-plastic behavior of FG cylindrical and spherical vessels under internal pressure is studied. For comparison with FG tanks, Elasto-plastic behavior of homogeneous tanks obtained. For this purpose, the assumption of ideal plastic behavior under axial symmetry conditions with using the Tresca criterion for the spherical and cylindrical tanks made of Al A359/SiCp is used. Power model is used for describe the gradual changes of mechanical properties in radial direction of FG material. It is shown that the analytically expressed results of the analysis of FG tanks after simplification coincide with homogeneous reservoirs. Furthermore, the bearing capacity of internal pressure will be higher relative to the homogenous tanks.