Abstract: This paper emphasized the transference features of beam waist D0 and far field divergence θ,defined by factor M2,while a light beam goes through a lens system A generalized parameter R(z) and q(z) are defined with the propagation factor M2 and plofile diameter of the light beam.Thefact is proved,that the parameter R(z) and q(z) obey the generalized ABCD rule.