The influence of small mutual displacements and turns of diffraction gratings that make up a compound grating on their summary reflected wave intensity in the Littrow mount was theoretically studied. It was shown that these displacements cause phase shifts between diffraction waves reflected by different gratings, that can considerable decrease their summary wave intensity. The admissible limits of displacements and turns, that enable to obtain maximum summary wave intensity were determined. The phases of diffracted waves were calculated on the base of coupled integral equation method.