The wavelength of the light will shorten when it travels in the refractive medium. Based on this property, a technique for fabricating high frequency holographic gratings is developed. It makes the grating frequency breakthrough the theoretical limit of 2/λ. The refractive medium is also used in the moire interferometry. When the frequency of specimen grating is 600 lines/mm, the frequency of virtual grating will reach up to 6000 line/mm and the fringe pattern of ±5 diffraction order can be obtained with the measuring sensitivity enhanced from 0.83 μm to 0.16 μm.