在大功率激光远距离定向传输中，远场发散角是衡量其性能的一个重要参量。大功率TEA CO₂激光具有功率高、光束直径大等特点，常规手段无法准确测量其远场发散角。为解决该难题，提出了一种利用激光光斑尺寸拟合分析法来评估大功率TEA CO₂激光的远场发散角。首先，从理论上推导大Fresnel数多模高斯激光束远场发散角，分析了影响激光束发散角的主要因素；然后，采用光斑烧蚀法试验测量近场(≤20 m)光斑数据，基于光束质量(M²)因子理论拟合得出了激光光束质量和束腰大小，从而推导出激光束远场发散角；最后，对比分析了以上两种方法的计算结果，讨论了结果存在偏差的原因。结果表明，近场光斑数据拟合法可准确、便捷地测量大功率TEA CO₂激光束远场发散角。

In the application of high-power laser long distance transmission, the far-field divergence is the one of important parameters to evaluate the laser performance. Conventional methods cannot be used to measure the far field divergence precisely because of the unique characteristics of TEA CO₂ laser, such as high average power, high peak power and large beam size. In order to solve this problem, a fitting analysis method was proposed to estimate the far field divergence of high power TEA CO₂ laser. Firstly, the far-field divergence of multimode Gaussian laser with large Fresnel number was calculated theoretically. Then, the near-field beam size(≤20 m) was measured experimentally using a spot ablated method, and the beam quality and waist radius were calculated based on the M² factor, and furthermore the far-field divergence was deduced. Finally, the results of these two methods were compared, and the deviation between the results was also discussed. It is indicated that the fitting method based on the experimental data is available to accurately evaluate the far-field beam divergence of high power TEA CO₂ laser.