The design, fabrication and applications of the 2.7 μm acousto optic Q switch have been introduced in this paper.TeO2 crystal has been used as the acousto optic interaction material and LiNbO3 has been used as the piezoelectric transducer material,the operation frequency of Q switch is 27.12 MHz.The experiment results show that the diffraction efficiency of the Q switch is up to 55% and the light transmittance is greater than 99% with respect to the laser wavelength of 2.7 μm at the driving power of 20 W.The sound absorption and heat radiation have been considered in the Q switch design.A water cooling mechanism has been designed and fabricated.The experiment verifies that the mechanism has good performance.