Abstract: Transient X-ray diffraction was used to diagnose the elastic deformation of the LiF single crystal which was shocked along the ［100］ direction. The experiment was implemented in Shenguang Ⅱ. High-intensity lasers irradiated a thin Cu foil to generate helium-like rays as X-ray source, another laser beam irradiated LiF single crystal which was 7 mm7 mm in size, 300 m in thickness as the shocked source. Image plate recorded the shocked diffraction signal of the lattice plane (200) as well as the unshocked signal. The experimental results show that the crystal lattice is compressed, lattice spacing in (200) decreases to result in shifting upwards. The positions of the diffraction lines associated with the (200) lattice plane indicate the compression along ［100］ direction by 11%. Whats more, the results show that it is useful for diagnosing the microscopic dynamic response of the material by transient X-ray diffraction.