Abstract: In order to deal with the problem of the laser gyro starting-up difficultly in cold condition, based on the principle of pre-ionization technique, the principle and specification of the LED exciting lamp is confirmed. The illuminance and energy distribution of cathode surface with different axial-installation position of exciting-lamp are calculated by the optical emulation software, and the layout of exciting light and axial-installation position is optimized. The experiment is developed which validated that the new-style exciting lamp units can significantly improve the ionization performance of laser gyro under cryogenic temperature, the ionization voltage is obviously decreased and the ionization time is obviously reduced. The one-time ignition success rate achievs 100% within -50~+75 ℃. The reliability of laser gyro was further enhanced.