- A new geometry for multi-peak diffraction survey of shock-compressed single crystal was suggested earlier (E. Zaretsky, SCCM’97, pp. 883–886). This geometry allows to obtain at least two diffraction peaks from different crystal planes in a single X-ray shot. In the present work a theory of multi-peak X-ray diffraction from arbitrary strained single crystal is developed. The theory allows to relate the shifts of the diffraction peaks produced by the different planes with the components of the strain tensor of the crystal. This technique was used for the interpretation of the pulse X-ray diffraction patterns obtained from shock-compressed single crystals of NaCl whose state during the compression was continuously monitored by VISAR. The obtained results allow to make some conclusion about the nature of the high-speed plastic deformation in shocked single crystals.