Laser gyro is an angle sensitive device. In order to overcome the lock-in phenomenon, a sine wave mechanical dither bias is introduced. In order to eliminate the error accumulation in the lock-in traverse moment, random noise is often injected into the dither driving signal. Until now, there is no good rule to select a suitable noise form, and long performance measurement must be carried out to evaluate the effect of noise injection. A new method is proposed, which can evaluate the effectiveness of noise injection in very short time. Results of experiments show that this method is very effective and can be used to select a good noise type.