Abstract: By using the method of generalized Huygens-Fresnel diffraction integral, the transmission analytical expression of flattened Gaussian beams in gradient-index media is deduced. The influence on the propagation properties of the medium gradient refractive index coefficient and the beam order is discussed. The results show that when flattened Gaussian beams propagate in gradient-index media, the intensity distribution on the axis varies periodically. Its change period is decided by the gradient-index coefficient, and has nothing to do with the beam order. The transverse intensity distribution of the peak on the axis is affected largely by the gradient-index coefficient and the beam order. The maximum on the plane with transversal intensity increases with the increase of the gradient-index coe