Within the frame of the Schroedinger formulation of light beam propagation, the ABCD law is extended to the so called effective ABCD system which effective beam quality factor is conservative. The evolution equations of beam width, curvature radius and effective divergence are derived, respectively. For the effective ABCD systems which second derivative of beam width square with respect to the axial coordinate is a constant, the nonlinear evolution equations of spatial coordinate operator and momentum operator are obtained by means of Heisenberg picture, respectively, and the corresponding Huygens integral is solved by a simple iteration method.