The roles of surface plasmon resonance and localized resonances in second-harmonic generation are investigated in a noncentrosymmetrical metallic film with a periodic subwavelength nanohole array. By using a recently developed microscopic classical theory and a three-dimensional finite-difference time-domain algorithm, numerical results show that the second-harmonic intensity is a function of the polarization and wavelength of incident waves. A peak of the second-harmonic intensity is achieved when the incident wave is along the direction perpendicular to the x-axis of nanoholes, which corresponds to the maximal extraordinary optical transmission. Meanwhile, the second harmonic is found to correlate with the group delay of incident waves.