We report a high-energy LD side-pumped Nd:YAG Q-switched laser with air cooling system. The peak power is 12 MW, and the pulse width is 11 ns when the repetition rate is 30 Hz. The repetition rate is tunable from 1 to 30 Hz with 1000 mJ pump energy. The optical-to-optical efficiency is 13.2%. The central wavelength is 1064.2 nm with bandwidth of about 1 nm. The beam quality facter M2 is 2.85. We adopt a semiconductor thermoelectricity cooling (TEC) system with fan air-cooling system, eliminating the need for a bulky cooling system as that in traditional high-power lasers. This offers the possibility of miniaturization of the whole laser system.