In the processing diagnosis of the inertiat confinement fusion (ICF), the ring coded aperture imaging technique is applied to gain high-space and time resolutions simultaneously. The key of acquiring high-spatial resolution is to obtain the point spread function of the imaging system correctly. The common method, firsthand projection method, neglects the X-ray diffraction effect, so the resolution of reconstructed image is decreased. Considering the X-ray diffraction effect the point spread function (PSF) of the ring coded aperture is derived from the scalar diffraction theory. And the Wiener filter is fabricated on the basis of the PSF. In National Key Laboratory of Laser Fusion, the imaging experiment on the diagnosis of ICF is completed using a ring coded aperture plate with inner diameter d1=250 μm and outer diameter d2=260 μm. The obtained coded image is processed by the Wiener filter where the diffractive effect is considered. The acquired reconstructive image by author's method is better than the image by the firsthand projection method.