腔内模式椭圆偏振态和磁场是激光陀螺产生磁致误差的两个必要条件，减小腔内模式椭圆率是降低激光陀螺磁灵敏度的重要途径。基于琼斯矩阵的谐振腔理论，提出了建立自洽方程的位置原则；提出了自洽方程求解中起振模式的选取方法；形成了准确、完善的腔内模式椭圆率计算公式。采用数值分析法，分析了平面腔激光陀螺反射镜参数及光路非共面误差对腔内本征模式偏振态的影响机理；提出了两种通过配置反射镜反射相移减小腔内模式椭圆率的新方法。

Ellipticity of modes in resonator and magnetic fields are two necessary conditions for magnetic sensitivity of ring laser gyroscope. Reducing ellipticity of modes is one of approaches to reduce magnetic sensitivity of ring laser gyroscope. Based on theory of resonator by Jones matrix,the positional principle of establishing selfconsistent equation is given, the method of choosing modes which exists is given, a theory of calculation on ellipticity of modes is formed. The mechanism of the effect of reflectors′ parameters and angle of folding plane of ring laser on ellipticity of modes in resonator are analyzed by analytical method of numerical value. Two new approaches to reduce ellipticity of modes are advanced, they are achieved by collocating the reflection-inducedretardances of mirrors. The results of research have important significance for study of engineering on reducing magnetic sensitivity of ring laser gyroscope.