Numerical simulations adopting the multiple-scattering method and experimental measurements demonstrate that it is practical to promote the coupling efficiency with the help of a 2D photonic crystal.It is found that higher coupling efficiency of waves generally appears at the edge of the photonic bandgaps. And resonance coupling of waves with relatively high coupling efficiency is likely to occur for the optical lattice constant of the photonic crystals approaching to the wavelength of the waves transmitted. Besides, there also exist many other frequencies that high coupling efficiency may be obtained. The maximum coupling efficiency may be as high as 1.89 times of that without introducing the 2D photonic crystal. Such an effect is especially useful for wave-coupling in optical integrated devices