In this study, the phase grating was investigated by using electro-optical characteristics of blue phase liquid crystals(BPLCs) such as fast-response and optically isotropic etc. The BPLC units was affected by distribution of periodically electric field and then changed the cubic structure into others, when applying voltage in etched electrode of grating pattern. A linearly polarized light is incident upon the sample and experience the periodic difference of index, and diffraction effect was generated. In order to find out the best conditions of these liquid crystals device, we discussed different factor such as angle of linearly polarized light, operating temperature of grating, cooling rate and electrode structure.