Using the single-atom induced dipole moment under strong field approximation as a source, we suggest a model to simulate the macroscopic high-order harmonic generation (HHG) from the mixed gases (He and Ne) interacting with intense infrared laser by solving the three-dimensional Maxwell’s equation of the harmonic field. Regular destructive interference (DI) and constructive interference (CI) are observed in the macroscopic HHG spectra when the gas jet is put at a good phase-matching position. A semiclassical model of short and long electron trajectories is applied to interpret the DI and CI of HHG qualitatively.