φ00 mm large aperture KDP crystal high power frequency doubling laser system for LF12 TW facility has been developed firstly. In the experiment of using doubling laser beam to target,the external frequency doubling conversion efficieny was kept over 60% when incident laser intensity was higher than 1.5 GW/cm2. Its highest efficiency of up to 65.6% was obtained. The largest output energy is 223.4 J (0.527 μm) with the largest input energy 357.8 J (1.054 μm).