本文详细分析了各种光场下光束质量M2因子。在不同的场中,A.E.Siegman当初所定义的M2因子,已经有了很大的变化,因而M2因子的特性也与当初不同,不仅M2因子可以大于等于1,而且可以小于1,甚至小于0。其反映的物理意义,也从经典场中的衍射极限倍数,变化为非经典场中的准直性量度以及对空间相干性的某些反映。此外还列举并分析了几种特殊的光束质量因子,最后讨论了M2因子应用的问题并指出了其局限性。 In this paper, the M2 factor of beam quality in various light fields is analyzed in detail. In different fields, the M2 factor originally defined by A.E.Siegman has changed a lot. Therefore, the characteristics of M2 factor are also different from the original ones. Not only the M2 factor can be greater than or equal to 1, but also less than 1 or even less than 0. The physical meaning it reflects also changes from the diffraction multiple of the classical field to the collimation measure in the non-classical field and some reflection on the spatial coherence. In addition, several special beam quality factors are listed and analyzed. Finally, the application of M2 factor is discussed and its limitations are pointed out.