提出了一种轴向不均匀热透镜的分段计算方案，将晶体沿着轴向等分为N段，每段均作为具有不同参数的类透镜介质，得到了晶体热透镜的正向和反向传输矩阵，以此确定谐振腔模场分布。分析了分段数目对于谐振腔基模束腰半径的影响。结果表明，束腰半径随分段数目的增加而变化，当分段数目超过某个确定值后，计算结果趋于稳定并接近实际。分别改变抽运功率、抽运半径及晶体掺杂浓度，讨论了腔模束腰半径达到稳定时所需的最小分段数目。

A method for modeling the longitudinally non-uniform thermal lensing is proposed, the laser rod is divided into N equivalent segments longitudinally for calculations, each can be dealt as lens-like medium, so both the forward and backward transmission matrix of longitudinally non-uniform thermal lensing can be worked out. A quantitative analysis of the fundamental-mode distribution in a plane-parallel cavity is made using transmission matrix. The effect of the dividing number N on waist radius of cavity mode is analyzed, results show waist radius changes with the number N, when N is larger than a certain value, waist radius will tend to stabilization and can get closest to realities. The smallest values of N for the waist radius getting to stabilization are discussed with the variations of the pump power, average pump radius and rare earth ion doping concentration, individually.