When a periodic object with subwavelength structure is illuminated by normal incident monochromatic parallel light, evanescent waves occurs. For the quick attenuation of the evanescent wave, the object with subwavelength structure cannot be imaged properly by ordinary method . However, one-dimensional periodic object with subwavelength structure can be encoded by a grating so that homogeneous waves can be obtained. Passing through the optical system designed specially, the well-distributed waves with evanescent waves information is enlarged so that it can be recognised by CCD camera. After that, the homogeneous waves with evanescent waves information is decoded by a decoding grating, the information of the encoding grating is filtered, and the image of the object with subwavelength structure reappears in the image plane. The imaging technique based on the conventional optical setup is novel for superresolution image of object with subwavelength structure can be obtained. Theoretical analysis of the imaging process and experiment is given well by photonic method. It is designed that where the encoding and decoding gratings are placed, so does how to choose the tilt angles between the two gratings and the object. The low\|pass filters used in the novel technique are also discussed. The results of experiments demonstrate that the theory is valid.