Abstract: A set of high stability high energy output three wavelength Nd:YAG laser system is designed. The system includes one oscillator, one amplifier and subsequent wavelength switching system. In order to solve the decline of output energy and stability caused by the laser rod thermal birefringence effect, a quarter wave plate is inserted between the output mirror and the laser medium. The output energy of the oscillator increase by 10% and the stability is obviously improved after the wave plate is added. When the repetition frequency is 10Hz, the energy of the 1064nm laser reaches 700mJ after amplification. The 532nm laser is acquired after the 1064nm laser passes through the BBO，and the energy is 325.6mJ. The energy of the 266nm laser is 84mJ after fourth harmonic generation . The pulse stability is less than 0.6% in one hour.

Key words: thermal birefringence