概括了光束质量的表示方法，由衍射极限倍数的定义出发，提出重点在于选取光斑直径，而且可把光斑测量归结到电子测试仪对剪切电平的测量上。给出了电子测试仪的测试原理，由所测光斑直径计算了氧碘化学激光器ＵＲ－９０腔的光束质量指标—衍射极限倍数，达到了１．２～１．６倍衍射极限，最后进行了误差讨论 Summarized the method of representing the beam quality, starting from the definition of diffraction limit multiplier, we put forward that the focal point is to select the spot diameter, and the spot measurement can be attributed to the measurement of the shear level of the electronic tester. The test principle of the electronic tester is given. The beam quality index - diffraction limit multiple of the oxygen-iodine chemical laser UR-90 cavity is calculated from the measured spot diameter, reaching 1.2-1.6 times the diffraction limit, and finally the Error discussion