A numerical iteration technique starting from the analytical solution of the fundamental wave and the second harmonic wave propagation equations in undepleted-pump approximation is presented for analysis of second harmonic generation in one-dimensional nonlinear photonic-crystal microcavities under pump light incidence at an arbitrary angle, accounting for pump depletion. Numerical results are in good agreement with experimental observation and theoretical predication by transfer matrix method. Analysis of the conversion efficiency of second harmonic generation in nonlinear photonic-crystal microcavities shows that dramatic enhancement of second harmonic generation occurs in the microcavities which have the optimal numbers of distributed Bragg reflector layers. The enhancement of nonlinear interactions is ascribed to mode resonance and localization of high intensity fundamental field, corresponding to the defect mode within the forbidden band of the photonic-crystal microcavities.