利用二维4路光纤激光环形腔被动锁相相干组束实验平台，对被动相干组束系统的光束质量进行了研究。以衍射极限倍数β因子作为光束质量的评价方法，理论分析了光束占空比以及不同锁相模式对β因子的影响，实验测量了对应不同输出功率水平的β因子。结果表明，虽然β因子可以在一定程度上反映出不同实验条件下光束质量的差异，但是由于β因子的测量核心是确定出焦平面处83.8%环围能量（功率）比的桶尺寸，不能反映相干组束远场光斑的特点，不适合用于评价被动相干组束系统的光束质量。比较分析了β因子与光束质量，光束质量能更好地反映出相干组束的特点。

Beam quality of the passive coherent beam combination system is studied using the ring cavity passive phase-locking experimental platform of four fiber lasers in two-dimensional distribution. With the times-diffraction-limited factor β as the evaluation method, the impact of duty ratio of sub-beams and different phase-locked patterns on the β factor is analyzed theoretically; and the β factor corresponding to different output power levels is measured in the experiment. The results show that although the β factor can reflect the difference in beam quality under different experimental conditions to some extent, it can not reflect the characteristics of coherent beam patterns in the far-field because the focus of the β factor measurement is to determine the bucket size of 83.8% encircled energy (power) ratio at the focal plane, therefore it is not suitable for the evaluation of the beam quality of a passive coherent beam combination system. A comparative analysis of the β factor and beam quality is done, beam quality can better reflect the characteristics of the coherent beam combination.