A graded photonic crystal formed by the varying the high-refractive-index square dielectric rods is used as a structured lens to focus.This lens can realize high energy utilitzation and large numerical aperture.Otherwise,the energy utilization and the imaging quality can be greatly improved by adding thin dielectric films on the two sides of the lens,and the energy utilization increases as the fill factor increases.A lens with an aperture of 100 μm and a focal length of 50 μm is designed for the wavelength of 10.6 μm.The energy utilization reaches 48.5% in the case of filling factor as 44.7% by finite difference and time domain (FDTD) algorithm,and the spot size approaches to the diffraction limit.