The main contribution of present study is carbon nanotubes (CNTs) agglomeration effects on the buckling behavior of multi-phases CNT/ fiber/ polymer/ metal composite laminates cylindrical shells under hydrostatic pressure. Governing equations are derived according to the Kirchhoff-Love’s first approximation shell theory and solved by a method composed of Galerkin method and Fourier series expansion. Equivalent elastic properties of multi-phases CNTs/ fiber/ polymer/ metal laminated (CNTFPML) cylindrical shell are obtained using Eshelby-Mori-Tanaka approach, considering agglomeration effects. Actually at the first, CNTs have been added to polymer matrix. After that, this new matrix has been reinforced by carbon or glass fibers. Finally, the composite layer has been joined with metal layers.The accuracy of applied method is validated with finite element method and an experimental test on carbon/epoxy and glass/epoxy composite cylinder under hydrostatic pressure, considering two methods of test.The results indicate that the CNT’s agglomeration, mass and volume fraction of CNTs and type of fibers play important roles on buckling resistance of multi-phases composite cylindrical shells.