In this manuscript, we consider the diffraction method of measuring the linear displacements of objects, which based on the formation the light field with defined phase distribution on the image plane of the monitored object. A functional scheme of the linear displacement measuring instrument has been developed. It realizes the suggested method based on a scheme of the Shack-Hartmann sensor. The prospects of using the Fresnel diffraction for linear measurements are shown in this work. Calculations and experiments show that proposed method allows measuring the linear displacement in the range of several millimetres with limiting error 0.005 % and displacement sensitivity up to 0.01 μm.