在考虑了时间平均能流密度的矢量特性的情况下，用修正后的光强公式重新给出了非傍轴标量光场光强二阶矩的表达式。在此基础上，在忽略了瞬逝波的近似下证明了：对于在自由空间稳态传输的单色标量光场来说，其横截面上的光强二阶矩随轴坐标z的变化成抛物线性变化。并进一步把傍轴光束的M2因子概念拓展到了非傍轴的标量光束。此外，还对一些相关的问题进行了讨论。

By taking the vectorial property of time average energy flow density and the accurate formula of the light intensity into accout, the first and second intensity moments of the nonparaxial scalar beams are defined. Based on the static scalar wave equation, the propagation law of the second intensity moments of monochromatical scalar beams in free space are obtained. A new beam qualty factor for nonparaxial scalar beams is introduced. Moreover, some important aspects of the intensity moments theory are discused.