The super lens with refractive index of -1 can achieve perfect imaging theoretically, but the photonic crystal with equivalent refractive index of -1 does not meet the conditions of permittivity ε=-1 and permeabilityμ=-1. The impedance of the photonic crystal does not match the free space, and the incident light at some angles cannot be coupled with the Bloch wave in the photonic crystal, resulting in the loss of these light information. It limits the imaging resolution. In order to improve the imaging resolution, a subwavelength grating is set on the surfaces of the photonic crystal and the coupling efficiency of the incident light to photonic crystal is improved. By adjusting the grating period, high spatial frequency components are involved in the imaging and the transmission of low frequency components is suppressed. With the subwavelength grating set on the surfaces, the imaging resolution of photonic crystal increases from 597 lp/mm to 850 lp/mm, which breaks through the diffraction limit.