Abstract: The noise characteristic and the stability of He-Cd lager at 4416Å have been investigated. The noise spectra and the relations between noise and discharge current as well as He pressure have been measured. The method of using the A-0 feedback at Brewster angle in cavity is introduced to reduce the noise of He-Cd laser and the results have been good. The A-O device is 6 mm thick quartz, 40MHz in frequency. The transducer is made of the crystal LiNbO₃, being operated in Raman-Nath diffraction to modulate the cavity loss according to the laser power, after operating che device, the noise ratio decreases from 6.3% to 1.5% and all the noise amplitudes tan be obviously reduced in the band from 2 Hz to 200 kHz, the fluctuation of laser output power comes down from 11.6% to 3.7% and the laser power decreases from 35mW to 30 mW with the optical loss 14%. By changing the discharge parameters, the high power with low noiso He-Cd laser having noise ratio 0.8% and output power 33mW may be abtained. There is no need to change the laser structure for this method, which may be applied on the He-Cd laser having higher power and other lasers.