Abstract: By redesigning the film with substituting SiO2 instead of MgF2 as the outer layer film,the frequency doubling anti-reflection coating on the KTP crystal is improved.After the KTP crystal with 1064nm and 532nm antireflection coating is applied in high power Q-switched Nd:YAG laser,any surface damage have not been observed even at intensity as high as 450MW/cm2 at a pulse repetition rate of 1kHz and 25ns of pulse duration.The experimental results show that both the surface quality and the optical property of the film have been improved.