The study of the first-order diffraction efficiency and the mechanism of formation have been investigated on dye-doped liquid crystals (DDLC) and liquid crystals with azo-dye-doped polymer film. The thesis mainly contains three experimental parts by changing the temperature of sample and the polarizations of writing and probing beams. The first part includes the study of temporal profiles of diffraction efficiency for transient gratings and their temperature and polarization dependence in azo-dye-doped liquid crystals. The dynamics of molecular reorientation of transient gratings can be understood by analyzing the build-up time of the peak efficiency and the relaxation decay of the first-order diffraction. The study of the polarization and temperature dependence allows us to understand the underlying mechanism of laser-induced transient gratings. The second part is concentrated in the diffusion process of photoexcited dye in a planar liquid crystal host. The experiment result reveals that the diffusion coefficient is larger for the molecular director along the grating vector than the perpendicular case and the diffusion will be faster as temperature increases. The third part is focused on the mechanism of formation and the temperature dependence of holographic grating for the liquid crystals with azo-dye-doped polymer film. The temporal profile of the first-order diffraction intensity shows a dip at the temperatures of nematic phase. The dip of the first-order diffraction intensity is temperature dependent and can be explained to be the light scattering due to the photothermal effect. The transient behavior in the dip of transmitted probe beam is also temperature dependent. The surface modulation has been measured by using atomic force microscope (AFM). The depth of surface relief grating of liquid crystals with azo-dye-doped polymer film is deeper than that of azo-dye-doped polymer film and the first-order diffraction efficiency is also larger for the liquid crystals with polymer film.