The double frequency characteristics of KBe2BO3F2（KBBF) crystals were analyzed. A new KBBF crystal grating coupler was designed with combination of the base wave grating coupling and the total reflection properties of KBBF crystals. The design principle of KBBF crystal grating coupler was introduced .By etching diffraction grating on the surface of a KBBF crystal, the diffraction order matching with the grating was chosen to generate double frequency. The total reflection in the KBBF crystal was used to increase optical path to obtain higher frequency conversion efficiency. Then, appropriate matching types were put forward by calculating matching angle, walk-off angle, frequency factor and other parameters. And the matched grating parameters were optimized to calculate groove parameters and diffraction efficiency of grating. Moreover, grating coupler frequency conversion formulas were given and their applicable ranges were shown. Finally, crystal grating coupler based on a 5.2 mm×5.2 mm×1 mm KBBF crystal was fabricated, and the results indicate that the grating coupler realizes double frequency outputs in deep ultraviolet waveband and its total frequency conversion efficiency reaches 16.86% .