针对具有锁相结构的圆筒组合型CO_{2激光器，分析了其注入锁定的原理，利用等价条形腔理论，建立了分析其输出基模的数学模型。利用该模型，研究了不同形变量对圆筒形腔输出基模的影响。结果表明，为了获得与注入光束模式类似的光场分布，复曲面镜与圆筒形谐振腔中平面镜镜面中心的形变量应控制在0.07倍波长以内。同时，分析在不同腔镜参数情况下腔镜形变对输出模式造成的影响，其结果有利于进一步优化谐振腔的参数设计。}

In the annular-combination CO2 laser with a phase-locking structure, the principle of external-injection phase-locking is analyzed briefly. By using the theory of equivalent strip resonator, the mathematical model to analyze the output mode is established. The effect of different mirror distortions on the output mode of annular cavity is studied. The results show that, in order to obtain light field distributions which is the same as the mode of injection beam, the mirror distortions of M1 and M′2 should be controlled at less than 0.07 times of the wavelength. Simultaneously, the effect of mirror distortions on the output mode under the different mirror parameters is studied. The results could help us to optimize the parameters design of this annular-combination resonator.