This paper presents a theoretical study on the influence of the geometry (layer thickness and length) and the magnitude of axially applied tension load on the delamination in a three-layer graphene/PMMA nanocomposite. Two different analytical solutions (Case 1 and Case 2) for the interface shear stress in the middle layer of the nanocomposite structure are obtained, based on the application of a two-dimensional stress-function method and minimization of the strain energy. The theoretical criterion for delamination in the interface layer, which is based on the model interface shear stress, is formulated. The obtained non-linear equation with respect to debond length is solved numerically, for both solutions, at different values of the mechanical load and geometry of the structure layers. For both solutions, it was found that the magnitude of the applied tension load influences strongly the appearance of delamination in the structure. For Case 1 (thinner PMMA layer) the delamination could be observed over 350 MPa external load; for Case 2 (thicker PMMA) it could be seen over 750 MPa. If the structure length decreases, under the above-mentioned conditions, the delamination begins at slightly lower values of the tension load. The magnitude of the applied load influences also the value of debond length. The obtained results could be used for fast prediction of safety intervals of applied loads and geometry design (without delamination) in similar nanocomposite devices to assure their safety working as sensors, nano- and optical electronic devices, energy devices, etc.