A stable and efficient all solid-state green laser with average power over 30 W is studied. The phase mismatching and thermal lens effect induced by local temperature rise of doubling frequency crystal are the major reasons affecting frequency doubling efficiency and laser output power stability. The method of grads-compensating temperature controll is used to adjust the operating temperature of frequency doubling crystal with large size. This temperature control system debases the inside and outside temperature grads of crystal to compensate the phase mismatching and thermal lens effect of frequency doubling crystal. This laser that is side-pumped by three bars laser diode array of 60 W and adopts the high efficiency flat-concave cavity, intracavity frequency doubling resonance structure, and acoust-optic Q-switching generates a maximum green average power of 31.6 W with 110 ns pulse width and 10 kHz repetition rate when pumped current of laser diode was 25 A and pumped power was 174.6 W. The optic-optic transition efficiency is up to 18.1%, and power stability is up to ±0.66% with beam quality factor of green laser M2=4.3.