Alpha functions are of critical importance to the cubic equations of state (EOSs) while most existing alpha functions are correlations in the empirical/semi-empirical formulations and limited to the bulk phase calculations. In this study, a new analytical alpha function and its nanoscale-extended formulation, which considers the strong intermolecular interactions under confinement effects, are developed based on the virial EOS and statistical thermodynamics. The proposed alpha functions, coupled with a nanoscale-extended EOS, are validated for a general use and be accurate to calculate the phase and thermodynamic properties of a wide variety of components in bulk phase and nanopores.