In this article, an analytical approach was developed for rectangular nanoplatelet reinforced composites. This approach could be used for estimating mechanical properties such as elastic modulus subjected to applied axial and thermal loads. Two sets of displacement were required for calculating the mechanical properties; thus, two sets of matrix/platelet displacement solutions, the far-field solution and the transient solution were precisely derived and superposed to achieve simplified analytical expressions for the matrix/platelet stress field components and the platelet axial stress field components in the entire composite system, including the platelet end region, by adding the imaginary platelet. The present research were compared and verified with the results of Mori-Tanaka and Halpin-Tsai and also, experimental results. The results were in good agreement with both experimental data and other published theoretical predictions. The present model was found to be very accurate and relatively simple in predicting Young\'s modulus of nanocomposites and was capable of correctly predicting effects of nanoplatelet aspect ratio, nanoplatelet weight and volume fraction.