Abstract: Ta₂O₅/Al₂O₃ laser gyro mirrors have been exposed in oxygen, air, argon and neon plasma respectively. Plasma was generated by capacity coupling Radio Frequency(RF) discharge technology. The effect of plasma pressure, plasma exposing time and plasma type on optical loss of Ta₂O₅/Al₂O₃ laser gyro mirrors was studied. The phenomenon and mechanism, for the optical loss change of Ta₂O₅/Al₂O₃ laser gyro mirrors was analyzed and discussed, by using comparing experiments, Energy Disperse Spectroscopy(EDS) and X-ray photo-electron spectroscopy(XPS). Ta₂O₅/Al₂O₃ laser gyro mirrors exposed in oxygen showed biggest total loss, which arrived 15 ppm(1 ppm=1×10^-6). The value was 2 to 4 times of Ta₂O₅/Al₂O₃ laser gyro mirrors exposing in air, Ne and Ar plasma. The total loss changing was caused by the absorption of outermost 2LAl₂O₃ layer in Ta₂O₅/Al₂O₃ laser gyro mirrors. When Ta₂O₅/Al₂O₃ laser gyro mirrors exposing O₂ plasma and Ar plasma alternately, the partial reversible changing phenomenon of 2LAl₂O₃ layer's absorption loss was found. The partial reversible changing phenomenon was discussed by XPS analyzing. The results show that the absorption loss changing is related to the exchanging of free oxygen and argon, occurred between outermost 2LAl₂O₃ layer and plasma. Some measures and suggestions are proposed to improve the stability of Ta₂O₅/Al₂O₃ laser gyro mirrors exposed in plasma.