This study investigates the buckling behavior of polymer-matrix nanocomposite beams reinforced with Carbon Nanotubes (CNTs) using the Finite Element Method (FEM) in combination with an analytical micromechanical model. The effective mechanical properties elastic modulus, shear modulus, and Poisson's ratio are first determined through the Mori Tanaka approach. Both aligned and random CNT dispersion states are considered. A distinct feature of this modeling is the inclusion of the interphase region arising from non-bonded van der Waals interactions between CNTs and the polymer matrix. The interphase is characterized by its thickness and an adhesion exponent, which together control the quality of interfacial bonding. After obtaining the homogenized elastic properties, they are imported into ABAQUS to perform buckling analysis of a cantilever nanocomposite beam (length 1 m, square cross‑section 0.1×0.1 m) subjected to a unit pressure load. The beam is discretized using 20‑node quadratic brick elements (C3D20) after verifying mesh convergence. A comprehensive parametric study examines the influence of CNT volume fraction (0–5%), CNT diameter (0.5–4 nm), temperature (260–350 K), interphase thickness (0.1–1.3 nm), adhesion exponent (0.01–95), and beam dimensions on the critical buckling load. Results show that increasing CNT volume fraction dramatically enhances the buckling load. For example, the first‑mode buckling load increases from 2.65 MPa for the pure polymer to 45.1 MPa at 5 vol.% CNTs when the interphase is included a 17‑fold improvement, significantly delaying buckling failure. Elevated temperature reduces the buckling load due to matrix softening. The interphase plays a crucial role: when included, decreasing CNT diameter (which increases the interphase volume fraction) substantially raises the buckling load; without the interphase, diameter has no effect. Increasing interphase thickness or decreasing the adhesion exponent (making the interphase stiffer) also improves buckling resistance. Longer beams and larger cross‑sections show expected trends of lower and higher buckling loads, respectively. For higher vibration modes (e.g., mode 5), hollow cross‑sections can exhibit higher buckling loads than solid ones. Validation against experimental data from the literature confirms that the proposed micromechanical model offers acceptable accuracy. These findings provide practical guidelines for designing CNT‑reinforced nanocomposite beams with enhanced buckling resistance.