An electro-optic Q-switched Tm:YAG laser with high peak power and narrow pulse width side-pumped by laser diode (LD) array is introduced. Using LGS crystal as electro-optical Q-switch, the characteristics of the laser output are investigated when thewhite Sapphire and Glan prism are used as a polarizer respectively. The results show that when using Sapphire stack as a polarizer, there will be a tail pulse with the increase of pump energy, however, when using a Glan prism as a polarizer, there is no tail pulse. Using a Glan prism as the polarizer, the central wavelength of the laser output is 2.02 μm, and a laser output with a maximum single pulse output energy of 60 mJ, a pulse width of 65.6 ns, a peak power of 0.91 MW and a slope efficiency of 5.41% can be obtained at a repetition frequency of 10 Hz.